Gyuki

Gyuki appeared in 2009 TV series called Kamen Rider Decade. His real name was Hibiki (ヒビキ) was Hitoshi Hidaka aka original Hibiki's incarnation from Kamen Rider Decade.

He is the master of the taiko-based Ongekido Hibiki Style (ヒビキ流 Hibiki Ryū) and thus Asumu's teacher, referring to him as Shounen (少年 Shōnen). Because he lost his righteous heart through his desire to become stronger, Hibiki is consumed by his Oni power and starts his metamorphosis into the legendary half-Ox Makamou and half-Oni, Gyuki. As a result, Hibiki adopts a lazy and rude attitude to most people, wears modern clothing, and even attempts to drive Asumu away in an attempt to retire from being an Oni. It is only when Kuuga is about to get killed by a Tengu Makamou that Hibiki decides to assume his Oni form and transforms into Gyuki as a result, wounding Ibuki and Zanki before being driven away by their pupils. Knowing that he will no longer be able to assume his human or Oni form again should he transform into Gyuki, he gives up his Transformation Tuning Fork Onkaku to Daiki Kaito to give to Asumu, who becomes the new Hibiki and slays his former master as his final request. After he became Gyuki completely, he attack Decade and Hibiki mercilessly before Hibiki attack him with Mouka Dotou form. In an imaginary scene between Asumu and Hibiki, Hibiki entrusts Asumu with Hibiki Henshin Onsa (which means entrusting the soul and also the license) and dies.

Because his desire to kill all Makamou is too strong, when he assumes his Oni form, Hibiki involuntarily becomes the legendary Makamou Gyuki (牛鬼 lit. Ox Demon), attacking any and all who get in his way. Later in Episode 19, Hibiki became Gyuki completely without becoming an Oni first. He is later finished by Asumu after Asumu decided to became the new Hibiki and defeat him using Mouka Dotou form, thus killing Hibiki.