Yuri Shibuya was just a normal Japanese high school kid on his way home from school he sees a former classmate of his, Murata, being bullied. He steps in to try and stop the bullies but they just grab him instead and dunk his head in a toilet in the girls' bathroom. Yuri is sucked into the toilet and ends up in another world. When he wakes in an unfamiliar area, Adalbert von Grantz unlocks the local language hidden in Yuri's soul. Conrad Weller then rides up and after a short fight Adalbert runs away. Conrad takes Yuri to a small village where he meets Günter von Christ who tells him that he is the new king of the Demon Kingdom. They then take Yuri to the castle where he meets Wolfram von Bielefelt and Gwendal von Voltaire, Conrad's two half-brothers (who do not look anything alike!).

While attending a dinner party that the former Queen is holding, Wolfram insults Yuri's mother by saying she is dirty human and Yuri reacts to the insult by slapping Wolfram across the left cheek. From everyone's weird reaction to the slap he finds out that this is actually how the nobles of the Demon Kingdom propose. Wolfram then throws his silverware on the floor to challenge Yuri to a duel to contest the engagement and Yuri unknowingly accepts by picking up a knife. Yuri is allowed to choose how they fight the duel and so he decides they should fight through a sumo match.

When Yuri wakes up after his first time using magic he finds out from Wolfram that Conrad and Gwendal have gone off to protect a human refugee village that is being attacked. Yuri convinces Wolfram to take him out to help. On the way they run into Adalbert who tells Yuri that it is humans that are attacking the town so it is a fight between humans. He tries to convince Yuri to come with him and leave the demons but Yuri decides he is going to help the demons. Yuri decides to become the demon king and when they return to the capital they hold a coronation ceremony. To complete the ceremony he has to stick his hand in a waterfall but when he does he gets sucked back to Earth.

Yuri awakens to finds himself in the girls' bathroom he originally disappeared from with Ken Murata in front of him with a police officer. Yuri decides to continue his interests in baseball by starting his own baseball team. While Yuri is at a baseball game, his mother, Miko, reminiscences about the past. After the game, Yuri is sucked back to the other world, where he finds out that some humans are threatening to start a war with them. Günter and Gwendal think it's a good idea for Yuri to hunt down the demon sword, Morgif, to make them so strong the humans will give up on wars.

Yuri, Conrad, and Wolfram set sail on a ship to Van da Via island where the demon sword, Morgif, is rumored to be located. On the ship there Yuri meets a ships apprentice named Rick, a merchant named Heathcrife and his daughter Beatrice. That night a group of pirates board the ship they're on. Conrad hid Wolfram and Yuri in a closet from the pirates but Yuri makes a cat noise and gets them caught. Yuri tries reason them that their actions are wrong, but when he sees one of the pirates dragging Beatrice he is angered and brings out his magic. He successfully repels the pirates with a monster made of the bones the humans have thrown on the ground. Conrad, Wolfram, and Yuri are put in a cell but Jozak frees them and they escape in a boat.

Conrad, Wolfram, Yuri, and Jozak reach the Van da Via island. At the inn they are staying at they learn about a legend of a cursed hot spring in the mountain and they decide Morgif is probably there so they decide to go investigate it. They find the sword at the bottom of the hot spring and Yuri attempts to grab it but it has a face and it bites him and so he runs away scared. They give up and return to the inn but later in the night he overhears a conversation between Jozak and Conrad and so Yuri goes back by himself to prove that he is worthy of being king and this time he successfully obtains the sword.

With Morgif now in his possession, Yuri finds out that the sword needs to absorb souls for energy. Jozak tricks Yuri to participating in a gladiator event so he can absorb souls when people die. Yuri is forced into a colosseum fight to the death and when he reaches the field he finds out that his opponent is Rick, the apprentice from the ship they were on.

While Yuuri is on Earth, Stoffel is in the other world hatching a plan. Yuri returns to the other world once again after a baseball game, arriving in the Original King temple's fountain. There he is met by his advisers, and the temple Maiden, Ulrike. Ulrike warns Conrad of an impending danger. At night, Conrad and his soldiers go to investigate some incidents of villagers being attacked. During the investigation, shadowy figures infiltrate the castle.

In the morning, nothing appears to have happened. However one of the soldiers found the door to the treasure room was picked. They find that the gem of the dragon king, that was part of a crown, was stolen. Yuri attempts to find the gem which leads to some comical events. During the search, the shadowy figures reveal themselves and try to kidnap Yuri. Conrad and Wolfram interfere and manage to capture one of the criminals and they find out from the interrogation that Stoffel was behind the stealing of the gem. Later at night Conrad, Wolfram, and Yuri set off to find concrete evidence against Stoffel.

As Yuri, Wolfram, and Conrad leave the castle to some soldiers, Stoffel and Raven start their next move. During the investigation, Conrad orders Wolfram and Yuri to stay put in a building. Yuri drags Wolfram and the remaining soldiers to conduct his own investigation of the missing dragon gem. Yuri's action led to his own abduction by Stoffel's men. Now Conrad and Wolfram head to Stoffel's castle to rescue Yuri.

Yuri wakes to find himself in Stoffel's castle. Stoffel tries to persuade Yuri to join his side, but Yuri rejects. As Gwendal and Stoffel prepare their soldiers for war, Jozak, dressed as a maid, manages to sneak Yuri out of his room by dressing him as a maid as well. Yuri gives their position away when he hears that a civil war is about to start. After Yuri reunites with Conrad and Wolfram, Yuri proceeds to stop Gwendal and Stoffel's forces from engaging. Yuri uses his power to stop the two armies from clashing. After the short battle, Yuri returns home to Earth.

Yuri goes to see a dolphin show, but when he is called up to the stage to shake hands with a dolphin he is then transported to the other world. After Yuri finds out about an imposter thought to be the Demon King, Yuri plans a trip to save the person, accompanied by Wolfram and Conrad. Along the way they met up with Gwendal. During the trip, they encounter a Sand Bear and Wolfram along with the rest of the soldiers except for Conrad and Gwendal fall into its sand trap. Yuri orders Conrad to rescue Wolfram. Gwendal and Yuri continue on to the country of Svelera. When Gwendal and Yuri stop at a town to gather water and provisions, they are mistaken to be an eloping couple and are chained together. They manage to escape.

Gwendal and Yuri enter the capital city of Svelera. When they enter a church they met Nicola, a bride, who then runs away from her own wedding ceremony with Yuri and Gwendal (both still chained together). A young boy gives refuge to Yuri, Nicola, and Gwendal from their pursuers. As they hide from their pursuers, Nicola reveals that she has the demon flute. Yuri tries to use it, but does not work. Their pursuers found their hiding place and so the boy and Nicola escape through the secret tunnel, while Yuri and Gwendal allow themselves to be captured as an eloping couple.

Gwendal and Yuri are sent to trial for Yuri eloping with a demon. Yuri is sentenced to work in the esoteric stone mines, while Gwendal is confined in a cell lined with esoteric stones. Conrad and Wolfram find the boy and Nicola who inform them of Yuri and Gwendal's possible locations. While Yuri was working at the mine, he sees some soldiers attempting to bury a beaten and bruised, but still alive baby. Angered by their actions, he then goes berserk and unleashes a mud monster on the soldiers. Gwendal manages to stop Yuri from causing any more damage.

After Yuri wakes up, he finds Norica digging through the cemetery looking for her son. Instead of a body they find the second part of the demon flute. As Yuri, the remaining women, and the brothers traverse the desert to escape the forces, they are trapped by the Sand Bear and prison guards. Yuri plays the Demon Flute which summons a storm that stops the prison guard army. Ryan then assists their escape with his partner, the sand bear. Back at the castle, Yuri tries to return home, but finds out he cannot go home.

After Yuri studies and practices baseball with Conrad, the news of a demon stone being stolen perks Yuri's interest. Yuri sets off into the city to find the stone with Jozak, Conrad, and Wolfram. They find the missing Demon Stone in the hands of Rosetta and her family, but the family is using the stone's power to repair magic tools and restore magic to earn more money for food. Yuri then decides to help them to get enough food. While they were helping Rosetta, they found that some thieves are trying to reclaim the demon stone. That night they find out that the thieves kidnapped Rosetta's brother and Rosetta set off with the demon stone to exchange for her sibling. Yuri, Conrad, Wolfram, Jozak, and Günter arrive in time to get the demon stone and save Rosetta's brother. Conrad decides to let Rosetta use the Demon Stone for business.

Stoffel and Raven attempt to appease Yuri by arraigning a celebration for him. Celi bursts into the room and declares she is marrying Raven, which shocks Raven and Stoffel. The past of Stoffel, Raven, and Celi are also revealed. During the ceremony, Ryan along with the sand bear, Keiji, arrive. Keiji's entrance however causes a sink hole which Stoffel, Raven, Celi, Yuri, Gwendal, and Conrad fall into. Raven and Celi reminisce their childhood memories at a crystal cave. Stoffel, Yuri, Gwendal, and Conrad find Celi and Raven. Then Keiji, Ryan, Günter, and Wolfram also manage to find them as well. Celi leaves again.

Yuri and Wolfram enter the guesthouse to get rid of some monsters. They both fall to the basement of the building due to weak floors. There they meet some caterpillar creatures that soon transform into their cocoon stage. Wolfram and Yuri have an argument about killing the monsters or letting them live. Meanwhile Gwendal and Günter search for Wolfram and Yuri. The building was collapsing, but then the cocoons hatch into bear bees and they keep the building from collapsing.

A fantasy world calls for a fantasy adventure, and Yuri has decided that he wants to see a dragon. He, Wolfram, Conrad, and Günter set out to the dragon preserve (dragons are an endangered species after all) to find one. Yuri quickly makes friends with one, just in time for some trespassing humans to attack looking to kill and sell a dragon. Unfortunately for Yuri, the group includes a young hero named Alford with a holy sword who decides to use the confusion to try and kill the "evil demon king".

Alford learns what it truly means to be a Hero. Yuri and the others find the dragons a new nest to help shield them from possible future poachers.

A young girl shows up claiming to be Yuri's illegitimate child, and then tries to kill Yuri. Yuri, compassionate as always, decides to give the girl the benefit of the doubt and assures everyone that there must have been a good reason behind it.

Greta spotted a man in town that she wanted to see again. Despite the fact that Conrad had told them to stay put, and still suffering from a twisted ankle, Yuri takes Greta into town.

The masked man turns out to be Hube, who now lays dying with Greta clinging to him. She tells the others that in her old home, Hube, who was in the dungeon, was the only one who would talk or listen to her.

Hube is returned to the Demon Kingdom and it seems that no one likes him. Greta tells Yuri that Hube had once told her that he'd done something unforgivable.

Hube once again attacks Yuri and Conrad defends him. Gwendal decides that Hube must die for his crimes.

Conrad thinks about how life seems to continue on, though more slowly, when Yuri is not around.

Yuri is suddenly pulled back to the other world but instead of ending up in a water source as usual he ends up in a barrel of alcohol.

Yuri soon learns that for the first time he is not alone. Somehow Murata has also ended up in the other world with him.

Yuri, Murata and Lady Flynn are on a ship carrying cargo, passengers and prisoners. They're heading towards Big Shimaron when it is attacked by Small Shimaron.

Yuri learns of the Four Forbidden boxes that will bring destruction. Murata seems to know a lot more about this world than he should, raising questions as to his true identity.

It seems Murata may be someone of importance. We learn that Conrad's arm may be the key to releasing the power of the box.

Ken Murata is something more than simply Yuri's friend; he also holds a high place in the Demon society.

Every four years the Ultimate Tournament is held and Yuri enters on Caloria's behalf.

The Ultimate tournament begins with Wolfram taking the first fighting position. After his battle Jozak battles with Adalbert who has entered this tournament solely for a chance to fight with Yuri.

Yuri is about to begin his battle, fortunately Lady Flynn is safe and he can fight the next opponent with all his might.

King Belar declares that Big Shimaron is the winner of this year's Ultimate Tournament and orders Caloria's representatives to be arrested.

The episode starts with Conrad's dream, where someone appears to him an arm. Yuri is back on Earth depressed thinking about Conrad. Then later meets Murata at the park.

Yuri and his group travel to Cavalcade and meet Mr. Heathcrife who can help them get into a secluded land called Francia.

Lyla, the king's helper, takes it upon herself to show Yuri and the others around and to help them look for the forbidden box.

Big Shimaron has taken control of Francia making escape hard for Yuri and the others.

Francia has made Conrad a prisoner and decided to join in alliance with the Demon Kingdom.

Yuri's older brother Shori reminisces about a time in Yuri's youth when he would call him his "big brother."

Baby Ernst, Eru for short, the son of Hube, and several other noble born children are gathered at Covenant Castle for the "Great Birth Ceremony."

A mysterious girl who bears a strong resemblance to Ulrike is seen being mischievous around town.

Stoffel has plans to set up Yuri with an appropriate princess thereby cementing his ties with the current ruler of the kingdom.

Yuri and co. have gone through lots of boxes in order to find the last box but coming up empty. They learn of a box in a lake and go to investigate.

Dunheely, Conrad's father, has trouble getting along with Gwendal especially when Gwendal despises him. When Dunheely has Gwendal join him in helping a secluded town of outcasts Gwendal must learn to see his step-father as the person he truly is.

After having their box stolen by the Maou, Big Shimaron finds a new way to impose power over the allied countries: an "overseas study exchange".

Adalbert has taken King Yuri hostage and demands to know if Yuri does in fact have Julia's soul.

Panic consumes the troops of both nations and Big Shimaron's king decides to leave the children he already has in order to escape the volcano's fury.

Maxine still has not given up hope of returning to his country and becoming wealthy and powerful. When he kidnaps Yuri and tries to escape he runs into one of Yuri's devoted subjects and is forced to abandon his plan.

When Yuri stumbles upon the "Demon Mirror" he's transported back to the time when Lady Celi ruled with the help of Stoffel. Yuri winds up meeting Lady Julia and comes to understand why she was loved by so many people.

Günter sets off on a "Nation Wide Tour" in order to better understand the "Common People." He comes to a town modeled after the old west and discovers that the town is full of fear and that only one person holding it together is a girl by the name of Gloria.

A man cloaked in shadows shows up wielding the power of the holy sword.

Yuri and the others go to check out the rumors about the Holy Sword and stumble upon a man possessed with demonic energy who wields the Holy Sword. Alford shows up in search of his sword and winds up helping Yuri and the others retrieve it.

A mysterious masked man with hypnotizing powers walks into King Belar's castle unhindered leaving us with many questions yet to be answered. Back in the Demon Kingdom Yuri is holding a party for the Alliance members.

Yuri is captured along with Wolfram and taken to Big Cimarion in order to be handed over to a hypnotized King Belar. Their transport is attacked by bandits who are led by a familiar face.

Yuri decides to confront King Belar and try to convince him to stop fighting. He goes off with his crew and Adalbert in tow towards the King's Castle.

Ulrike reveals that the final forbidden box is on Earth. Yuri, along with Murata, Wolfram, Conrad and Gwendal set off to locate and bring the box back to The Demon Kingdom.

Yuri takes the group on a sightseeing trip while waiting for Bob, the Maou of the Earth to contact them. Shori meets up with Rodriguez, who ask a favour from him.

Yuri and co. travel to Switzerland after discovering that Bob is currently staying there. Yuri is shocked when he finds his parents followed him there and they travel together to meet Bob on a bus that was sent to fetch them.

Yuri and Bob battle with magic and Yuri wins. Bob decides to entrust the final forbidden box to Yuri.

The Kohi and many animals are acting up due to the fear of all of the forbidden box's are gathered together. Yuri manages to gain their trust and calms them.

Günter is poisoned again and Suzanna Julia's retired father visits the Demon Kingdom to release him and him and Yuri talk of Julia. But then, Günter's body unexpectedly moves on its own.

It seems that one of the maids has been affected by miasma, a disease that makes the person unable to trust anyone. Yuri, Wolfram, Jozak and Conrad must obtain a rare herb on a mountain to cure the maid but how will they succeed if they are affected by it too?

Yuri along with Conrad, Murata, and Wolfram travel back to earth in order to get something Yuri left behind. They are unable to return to their world because of the box removed from Earth and they travel to Switzerland where Bob is to ask for assistance.

Human villagers decide to build a bridge between the land of humans and the Mazoku. But they are being attacked by mysterious light wolves believed to be the ghosts of the war 20 years ago.

Günter teaches Yuri about the past of The Great Demon Kingdom. The founding king Shinou, the Great Sage as well as the four families with the keys to the boxes are shown. Afterwards, Wolfram seems to be acting strangely.

Shori goes to The Great Demon Kingdom by accident after the lake in Switzerland pulls him in. He asks Yuri to stop the ceremony of the forbidden boxes and questions the Original King's decisions.

A possessed Wolfram offers to give Shori magical power to protect Yuri but before Shori can answer, an unexpected visitor arrives interrupting the conversation.

Shori can now manipulate water and practices. Miko attempts to go to her sons in scuba diving equipment and ends up dragging her husband into freediving. While practicing, Shori loses some control.

Yuri forgives Shori for his misdeed and consoles him by telling his admiration for him to use maryoku and recover so quickly.

Yuri starts the ceremony but Wolfram suddenly attacks Yuri, distracting Yuri into messing up the ceremony. A dark figure appears and takes Conrad's left arm.

Shinou praises his handpicked strategist and Wolfram is taken to Blood Pledge and Greta wonders if he had died. Anissina speculates that Wolfram still is alive and plans to freeze his body like Günter's when he was poisoned.

Yuri and co. head back to The Original King's Temple to retrieve the keys from The Original King. However, they are attacked by Soushu's army of dolls when they enter.

Soushu enters Yuri's body to take it over from the inside. Conrad, Gwendal, Jozak, Hube and Günter awaken outside the temple and return to the castle, where Wolfram had been revived with his heartbeat returned to him.

Soushu has successfully taken over Yuri's heart by revealing why he chose him as the Maou—to be his body. Meanwhile, Günter and Dorcacos travel to Morgif's birthplace in order for him to reveal his true powers.

Soushu is forced out of Yuri's heart and Yuri defeats him, causing Soushu's troops to disappear as well as Shinou's soul together with him who thanks him. Murata told Yuri that they can not travel again to the other world because Shinou had disappeared.

Yuri and Murata return to The Demon Kingdom. Günter is preparing for the Maou's 16th birthday where Yuri will determine his path as an adult, Wolfram is on his way back from the Bielefelt lands. It turns out that while Yuri was away, the Ten Noble Family had chosen a new Maoh, which turns out to be Wolfram!

Yuri goes through with the ceremony and soon finds himself in The Original King's temple where he has to make the final decision. He meets The Original King himself, who tells Yuri that he will eliminate anyone who dares oppose Yuri being king.

After Yuri's decision is final, Wolfram brakes off the engagement in order to avoid any conflict and returns to the Bielefelt lands. Yuri pursues him and they have a duel. Yuri then uses his powers to defend himself and Wolfram, and to prove he is worthy of being king.

When merchants come to The Demon Kingdom's capital to sell miniature bearbees, the whole town is turned upside down. Greta convinces Yuri and Wolfram to buy her one, but the merchants give her one piece of advice: never get her bearbee soaked in water. They soon discover why.

During one of his study sessions, Yuri receives an invitation to attend Lyla and king Antoine Jean Le Pierre's wedding. However, the king announces that the special sword of his country, the one needed for them to get married, had gone missing. Yuri promises to find the lost sword.

Murata, Jozak and Conrad travel to Big Shimaron to obtain something that Murata had left behind without Yuri's knowledge. Yuri and Wolfram find out and follow them in Celi's ship.

Yuri and Wolfram attends a banquet disguised as girls. It is there where Yuri meets Saralegi for the first time. Yuri was exposed while Wolfram escaped with Adalbert's help.

Murata, Jozak and Conrad infiltrate the castle and manage to find a box full of swords. When an intruder alarm is sounded, Murata discovers it was not them that had been found.

Lanzhil, in order to get rid of both Conrad and Yuri, orders Conrad to execute Yuri to prove his loyalty to Big Shimaron, knowing that he would not do it.

Yuri and co. visits the academy where Conrad trained to become a soldier.

It turns out that Anissina's brother has set her up with a suitor for her to marry.

Yuri, while visiting Caloria, was attacked by members of the White Crow but fortunately was saved by Al while Wolfram and Conrad were busy fighting.

While trying to obtain the swords, Yuri and co. were tricked and attacked by the White Crows.

Yuri, Conrad, Wolfram and Murata returns to Earth so that Yuri is able to take his final exam.

Greta's past is revealed.

An old invention that was created a long time ago is found.

Sara invites Yuri to Small Shimaron to make an alliance with The Great Demon Kingdom. They were attacked while having a discussion.

Yuri and Sara returns to the latter's castle where Yuri meets Sara's trusted subordinate, Gerard.

Sara is captured while Yuri manages to escape with the help of his subjects but Yuri is determined to go back and save Sara.

Big Shimaron has crossed over to Small Shimaron to capture Yuri.

It is revealed that Berias is the one who shot the arrow under the orders of Sara so that he can gain Yuri's trust.

After Yuri went to Small Shimaron, the heads of the ten noble families summons him to a meeting around the round table to know his motives. However, the meeting is shortened when Yuri decides to play a game of "Shinoued Away" with them.

Just as Yuri and Murata are about to head for The Great Demon Kingdom, Shori surprises them as he jumps in with them and ends up pulling them further away than they planned.

Shori chases the White Crows and manages to rescue El by using magic.

As Jeneus is about to escape with Shori through a ship, Yuri and co. arrives and attempts to stop him.

Murata informs everyone that his memories of his past life has been transferred to Jeneus and that Jeneus is just a copy of the real person from the past.

Alazon explains the history of Seisakoku to Shori while Yuri and co. takes refuge at a hideout prepared for them.

Shori follows Alazon and unleashes the power of the sword on Big Shimaron's army which had come to destroy the White Crows.

The Ten Nobles gathered together to have a meeting and questioned Yuri's motive to travel to Big Shimaron. They were suspicious of Shori and placed him under house arrest for associating with the enemy.

Big Shimaron is approaching faster than everybody thought and Waltorana's troops has been mobilized. When Yuri, Murata and Shori attempt to get to Lanzhil's ship, they overshoot and arrive on Sara's ship instead.

Murata and Shori stops Yuri by pushing him overboard, sending him back to Earth along with Shori while Murata is transported to The Original King's Temple. When Yuri awakens, he finds himself unable to return to the other world.

When Yuri comes back, he realizes that Conrad is still in Big Shimaron and Wolfram has gone to fetch him back.

Yuri sends a letter to Sara, informing him on the capture of Beria and inviting him to The Great Demon Kingdom to get him back.

Berias explains the past of Seisakoku to Sara.

Jeneus attacks The Great Demon Kingdom in order to see The Original King once again as his last wish. He sends monsters as decoys to The Great Demon Kingdom and travels over to The Original King's Temple.

Yuri invites Alazon to Covenant Castle as an honored guest. He agrees to help Alazon to the exasperation of his subjects.

Sara appears in an alleyway with the Holy Sword lying next to him. When he takes out the sword, it leaves a faint trail on the ground. Sara follows it and finds Jeneus.

The Original King decides to disappear along with Jeneus but Yuri intervenes. After Yuri had lectured The Original King, they had let down their guard and Jeneus stabs The Original King.

Everything has turned back to normal but anxiety hangs in the air as Yuri has not awaken. Sara appears, offering to help Yuri with the Holy Sword.