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!).

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.

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.

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.

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.

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

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.

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.

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.

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We don't have an overview translated in English. Help us expand our database by adding one.

We don't have an overview translated in English. Help us expand our database by adding one.

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.