Yuuri is the youngest of his family. His brother is the leader of a demon tribe on Earth, and his father is a Mazoku. His mother, Jennifer, had always wanted her children to have wings just like demons were usually depicted in Japan. However, to her dismay neither child had black wings. When Jennifer was in labor, she met a younger Conrad that was sent to Earth to inform Yuuri's father that King Shinou (the first King of the Great Demon Kingdom) had ordered that the twenty-seventh Maou be born on Earth; Conrad helped her get a taxi and named him Yuuri, but much to his dismay, his name is a Harajuku-pun. While he was growing up, his mother had always thought that he looked cuter as a girl, so when he was a baby through his toddler years he wore ribbons and was made to look "cute". Yuuri's favorite sport is baseball, he used to play in Junior High until he got kicked off the team.
One day, he was watching the high school play before he saw his friend, Murata Ken getting beat up. Trying to save him, Yuuri found himself abandoned and being dragged to the girl's bathroom to get his head flushed. Funnily enough, it's through here that Yuuri was transported to the Great Demon Kingdom. Once there he regained consciousness in a human village. Confused and dazed, thinking that he was in a RPG he started to talk to a woman, and the is is when he first found out abut his features. A man called Adelbert found him. Later on Conrad, the name who named him, saved him from Adelbert and he is taken to the castle. After he arrives, amazed of who his really is, he met Wolfram, the son of the Maou before him. During dinner, Wolfram expresses how much he disagrees with a half-human Maou and insults his mother. Yuuri gets upset and slaps Wolfram across his cheek; a custom in that nation s a proposal. When Yuuri refuses to take it back, the engagement is finalized. Wolgram challenges him to a duel, and Yuuri freaks out. Conrad steps up and tells Yuuri about using his strengths and what he knows. Instead of dueling him with swords, Yuuri challenges him to a sumo match and wins. Wolfram retaliates and uses magic, injuring some people. This is when Yuuri's Maou form first takes form. He controls the water around him, binding Wolfram in the word JUSTICE. It is then that Wolfram becomes obsessed with him. He sneaks into Yuuri's bed and wears a pink negligee, often making it hard for him to sleep and taking form in his dreams. He gets called "wimp" a lot, and not much respect from him as he gets from Gwendel, Gunther and the others. Wolfram's mother hits on him a lot. He says that as Maou, he will unite the kingdoms, just as the first Maou did so that humans and demons can live side by side and there can no longer be war. The others stand by their king, though sometimes they fully do not understand.
Later on, he and Wolfram go into the guest wing of Blood Pledge Castle to get Wolfram a room for himself and they find themselves surrounded by cocoons. The Bearbees, a very rare species hatche from it and Wolfram declares them a product of their love. Later on, after a long journey looking for a demon lord, they adopt a daughter named Greta. Much to his chargin, Wolfram says that after they are married, their family will grow.
It is revealed that there are four forbidden boxes in the Kingdom, sealed away by Shinou and his advisor (reincarnated as his friend, Murata) which require four keys to open and operate them. Yuuri manages to stop a rival nation, Big Shimaron from using one called End of Earth by removing the key (Conrad's arm which was lost trying to protect Yuuri). They set out on a quest to stop all of them. In his revenge, the evil spirit that had been the reason why Shinou created the four boxes returned and tried to open them all again. The spirit, Soushu, in his final act of revenge, stopped Wolfram's heart until Yuuri defeated him. Once that was over, Yuuri had little time before he was sent back into his own world.
Yuuri's entrance to Template takes place here, where for great laughs, King Shinou decided that Yuuri would die along the way and end up in the city.