Yuuri Shibuya, after helping out another student who was getting picked on ended up getting flushed down a toilet to another world. After meeting Adelbert, he finds out that he is the new Maou (demon king). Conrad comes and saves him, taking him back to a nearby village where he meets Gunter. Here, he learns more about where he is and what the Maou is.

Yuri arrives at his new castle home in Shin Makoku and immediately makes a less than impressive first impression on Wolfram and Gwendel. Some dinner, insults at Yuri's mother, and a slap to the left check later, Yuri finds himself not only challenged to a duel, but engaged to Wolfram! Gwendel quietly uses the duel as a chance to test the authenticity of Yuri's Maou spirit. Needless to say, Yuri will win and all disperse all doubt...right?

Wolfram takes Yuuri to an outlying village where Conrad and Gwendel are dealing with "a human threat". On their way there, they come across Adelbert, who attacks Yuuri. The quarrel is resolved; Adelbert escapes. Yuuri gets to see first hand the animosity between humans and Mazoku. When a little boy is injured trying to get a human criminal away from Yuuri, Yuuri finally realizes why he should become the official Maou of Shin Makoku. He aims to bring peace between the humans and Mazoku. His coronation involves putting his hand under a mini-waterfall. Contact with the water draws Yuuri back into his own world, back to Earth, and he finds out that no time has passed since he left.

The humans are wanting to have war, so Yuuri, Wolfram, and Conrad set out to find "Morgif", the ultimate weapon that only the Maoh can wield.

Conrad, Yuri and Wolfram are on the boat traveling to the Island where the demon sword is to be found. Wolfram has stowed away on the ship. Yuri has to try to pretend to be human using a disguise as the are on a human boat. He makes friends with a poorly treated cabin boy and in the evening the ship is attacked by Pirates. Yuri as the Maoh now has to save the day.

Yuuri, Conrad, Yozak and Wolfram arrive on the island and have to trek all the way up a mountain. They find Morgif at the bottom of a lake of boiling water and Yuuri has to dive in and get it. He's too wimpy at first, but after overhearing a conversation between Yozak and Conrad he goes after it again on his own and overcomes his fear.

Yosak registered Yuuri to fight in a colossium to get a lot of human spirit in one time. Morgiff awoke and went wild. Yuuri heard Morgiff talking to him, he called Morgiff's full name to control him. After he got the control, he along with Conrad, Wolfram and Yosak escaped from the city to find that Lady Ceci has been waiting for them. Once they got into her yacht, Yuuri overheard Conrad and Yosak talking about him. Conrad was angry that Yosak put Yuuri in danger, Yosak said that he only wanted to test the new king. Yuuri gave Yosak the stone in the middle of Morgiff's forehead, which was the source of the sword's power. He told Yosak to hide it or do whatever Yosak thought was good for the sake of the kingdom. Yosak was quite surprised and touch that Yuuri trusted him and agreed to do the task.

While Yuuri is on 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 impeding 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 capitol 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. To recover from a twisted ankle he received during the assassination attempt, Yuri along with Conrad, Wolfram, and the little girl head to Hildyard to visit some healing hot springs. The city looks fun, but who is the mysterious, masked bodyguard and why does the little girl seem to know him?

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. Yuri gets a sense of Déjà vu when he stops to defend a girl from some bullies and she promptly runs away. Yuri grabs Greta and runs and the same girl that ran saves them. However they are eventually caught. They get away from the cell, but while being chased they are saved by Conrad and Wolfram. Then a man Yuri met on the boat to Van da Via, Heathcrife, shows up wanting to get back all the property in this town that a man named Vuillon swindled and forced from their owners. After a masked man attacks Yuri, Conrad steps in to protects Yuri and fights him. But who is this masked man? And can Conrad defeat him?

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. Yuri wants to heal him but Conrad tells him not to. Wolfram does only because it's what Yuri wants. The next day Yuri and the others go to a rare animal race. It turns out that after the fight between Conrad and Hube that Yuri demanded that Vuillon return everything he swindled from the people. Vuillon said he would if Yuri could beat him in a gambling contest. The stakes, if Yuri wins he'll return everything, if he loses Yuri becomes his! Conrad assures him that he'd pick him up and run if they lost. It seems it would be a race between Vuillon's Hell's Paradise Goala, that looks like a giant Koala bear, and Ryan and his Sand bear, Keiji. It seems that not only can the Goala run very fast, it's also carnivorous. Can Keiji and Ryan outrun and defeat the Goala or will Conrad have to keep his promise and take Yuri and run for it?

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. But what? Then they hear that it has something to do with a woman named Julia. But who was she? Yuri learns through Gisela what exactly happened to Julia and why everyone blamed Hube.

Hube once again attacks Yuri and Conrad defends him. Gwendal decides that Hube must die for his crimes. Both Greta and Nicola do their best to try and help Hube. But will their help be enough? Will Hube be killed or will he live to see his child born? After Nicola's baby boy is born Yuri decides to adopt Greta. Yuuri is finally able to return home.

Conrad thinks about how life seems to continue on, though more slowly, when Yuri is not around. He recalls a tragedy at the end of the war 20 years ago, and remembers the time he went to Earth to deliver the Maou's soul to a certain mother-to-be.

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. Günter and Conrad soon arrive with Greta in tow. It seems there's unrest with the humans wanting to start a war and that Conrad and the others did not summon Yuri this time. If anything they are more desperate to send him back to Earth! Greta was riding with Conrad and Yuri with Günter when Günter is shot by an arrow! Conrad instructs Yuri and Greta to go to the church but as soon as he locks the door these weird guys with guns show up! Conrad tells him to throw holy water on a painting and that it will send him home. However during the battle Yuri witnesses Conrad fight and then lose his arm before he's knocked into the painting. He is sent home... or is he? What happened to Conrad and Greta did they make it out of the fire too?

Yuri soon learns that for the first time he is not alone. Somehow Murata has also ended up in the other world with him. They are told about the owner of a nearby castle and go there. Adalbert and a man named Maxine also show up. Yuri hoped that Adalbert would not recognize him with a hat and sunglasses on but he does. When the country's guards appear Adalbert and Maxine run but then Yuri realizes that the weapons are the same as the ones from the battle Conrad was in. Upset, he uses his magic and takes care of the guards. Meanwhile Jozak who'd been in disguise in the same town sends a letter informing The Demon Kingdom of Yuri's location. Meanwhile, Günter's body recovers but now he has to deal with a new form for his soul to live in while his body recovers.

Yuri, Murata and Lady Flynn are on a ship carrying cargo, passengers and prisoners. They're heading towards Big Cimaron when it is attacked by Small Cimaron. Lady Flynn not wanting to lose Yuri, grabs him and they go overboard. Murata goes in after them, not wanting to be left alone. Jozak, in disguise, then releases all the sheep and prisoners. The sheep can become big flotation devices. But now that they're on land, are they really safe?

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. Murata and Jozak devise a plan to rescue Yuri and escape. However, in the end, when Murata's life is in danger, Yuri refuses to run away and leave anyone behind again.

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. Yet, if it's not the right key, then the box will become out of control. If the box gets out of control, does Yuri have what it takes to stop it?

Ken Murata is something more than simply Yuri's friend; he also holds a high place in the Demon society. Thanks to Jozak, Gwendal comes to Caloria bringing with him aid for the wounded and homeless. Despite not wanting help from the Demons, the citizens of Caloria grudgingly accept their help after some persuasive talks. Finally a messenger arrives from Big Cimaron informing the populace that the Ultimate Tournament is about to begin.

Every four years the Ultimate Tournament is held and Yuri enters on Caloria's behalf. In order to qualify for the tournament he must win the preliminary race from East Nilson to Lambeil. Yuri races to become the winner of the preliminary but as he soon finds out many challenges await him including Maxine with his vengeful manju attack!

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. The group runs into trouble when Lady Flynn is captured and held as ransom for them forfeit the tournament. What can Yuri do to help Lady Flynn and who is the masked lady that claims to protect love?

Yuri is about to begin his battle, fortunately Lady Flynn is safe and he can fight the next opponent with all his might. But as he soon finds out his battle will become very complicated when someone he trusts is fighting on the opponents side. And when Adalbert joins the battle Yuri winds up fighting for his life!

King Belar declares that Big Cimaron is the winner of this year's Ultimate Tournament and orders Caloria's representatives to be arrested. This leads Yuri and the others to make an escape with the help of Fanbalen, Lady Celi's current love interest. With Fanbalen's help they are able to escape with the box The End of the Wind in tow. Conrad is not with them and it looks as if he will not return to the Demon Kingdom.

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 tries to get Murata to help him get back to the other world, Murata decides to help Yuri back to the other world. When they reach the other would, Wolfram, Günter, Greta and Ulrike are there to greet them. Gwendal soon shows up and apologizes for Conrad's misconduct assuming he will get punished. It is revealed that Murata, or rather the great sage was the one who made the 4 forbidden boxes, so in turn Yuri wants Murata to explain them a little. As well as their connection to the Weller Family. Conrad is reading when he is summoned, he is soon informed that Big Cimaron is in contact with another Box. Yuri and the others become aware that Big Cimaron is after another Box and goes after it as well.

Yuri and his group travel to Cavalcade and meet Mr. Heathcrife who can help them get into a secluded land called Francia. The king of Francia refuses to choose either the Demon or the Big Cimaron side. Conrad with his Big Cimaron goons are also in Francia and are also after the box. Will Günter accept Conrad's betrayal or will he be forced to kill him?

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. After many hours of fruitless searching Yuri and the others are told that the box has been found in an old esoteric training ground. However when they arrive at the ruins they find the troops of Big Cimaron waiting to ambush them. Will they escape from this trap and manage to find the forbidden box?