|Manga Debut||Chapter 22|
Yamaha is an elite demon, and an ally of Legato.
It's hinted that he was Mephisto Barto Kucabara and Funi's schoolmate in the School for Aristocrats, as he knew him as a kid. A year before the start of the series, Yamaha kidnaps Bchuler along with a fellow demon, following Legato's plan to eliminate Kucabara. Yamaha gets Funi to lie to Kucabara, telling him that Bchuler had fallen into the human world while watching a solar eclipse. After Kucabara jumps into the portal in an attempt to save his friend, Yamaha appears to Funi, expressing his disgust for the fact that a virtuous demon like Kucabara could become king, as he had "committed a great sin".
Despite that, when he and Legato watch Kucabara fight the king's special forces from the demon world, Yamaha shows some admiration for the prince's power, even asking Legato if they should call in reinforcements. Legato says that there is no need, as they were "directing a beautiful performance" for Kucabara's end. As Dukon is killed by the elite soldiers, Kucabara's rage causes him to transform into his full-powered state, and the sight of several wolf soldiers being killed impresses Yamaha even more. Legato states that, since Kucabara was "able to overcome the wall of the devil even with a pure heart", the reasons to kill his brother had "increased by one".
Yamaha then goes with Legato to the human world, where they confront Kucabara with the still bound Bchuler. With the revelation that his brother not only hated him and had been concealing his strength, but also had been involved in the other princes' murder, Kucabara is distracted. Using the distraction, Legato uses his Soul Chain to bind him, summoning his blade and stabbing him and saying he would be the next king of the demon world. Kucabara makes a deal with Legato to keep his life in exchange for power, and Yamaha returned to the demon world with Legato, Funi and the rest.
Soon after Kucabara's arrival at Father Seruma's abbey, Yamaha commands many demons to attack Idamaria. She tells a weakened Kucabara that the target was her, and that he should go away, as he was being a hindrance. At that point, Yamaha, who had been concealed between the demons, reveals himself at the mention of the demon prince, leaping in the air and barely missing the two with a powerful attack of his blade. Idamaria briefly clashes with Yamaha, and soon notices the difference between him and the demons she had fought before, startled by his strength after being pushed away by his attack. Yamaha assumes that Kucabara has exchanged event horizon for the human world, and had become an underling of Idamaria.
He attacks them both with a powerful technique, a massive, explosive slash that causes Idamaria to dodge and leaves Kucabara open. Yamaha brings Kucabara to the ground, holding him down by the neck and talking about how "the demon world's strongest devil" had ended up "pitiful and unsightly", and revealing that after getting his brother's black matter, Legato "became the legitimate successor of the demon king". Eventually, Bchuler kicks him away from Kucabara, and uses the dark matter he still had on him to transform, in order to take revenge on Yamaha. Bchuler's Dark Tornado is blocked, but manages to throw Yamaha against the trees behind him and into Jupiter's room.
Yamaha recognizes that was a fight he couldn't win, and decides to kidnap Jupiter, taunting Kucabara, Bchuler and Idamaria to go to the demon world and attempt to rescue her. With a slash, he opens the portal, and is surprised by the combination of Kucabara's lunge and Idamaria's Holy Storm. The two end up colliding into a large explosion, and Yamaha loses his focus. Father Seruma swiftly cuts off Yamaha's left arm in his moment of distraction, taking Jupiter from him. In turn, Seruma gets distracted scolding Idamaria, and Yamaha uses the opportunity to throw several skull-shaped bombs at him, taking Jupiter back and walking right into the portal and giving them 3 days to come after her, or he'd throw her into the Burning Hell. Idamaria attempts to reach them, but the portal closes.
Back to the demon world, Yamaha and his unnamed ally carry Jupiter to Legato, but encounter Garypeter Sugal and an unnamed shinigami in the way. Yamaha taunts Sugal, speaking of his recent encounter with Kucabara and asking him if he was even any use in the human world after losing his rank of shinigami. When Sugal walks past the two, Yamaha tells him to not ignore him, at which his ally attempts to calm him down. Exactly what elapsed next is unknown, but Yamaha lays dead on the ground with a wound on the back of his head (caused by Sugal's blades) and eyes wide open, and his ally calls Sugal a coward, as he had attacked them from behind. When asked the reason why he attacked them, Sugal states that the the way they approached things was "lacking mathematical beauty", as they were bringing "disgusting and living" humans into the demon world.