Hibiki's World
Asumu / Kamen Rider Hibiki
Asumu is Hibiki's child apprentice, wanting to become a full-fledged Oni just like his master Hibiki in the taiko drum-based Hibiki Style of Ongekido. Asumu is the only student of the style. Before inheriting Hibiki's powers Asumu was able to assume a form similar to Transformed Kyosuke called Transformed Asumu. As a result of his master losing the ability to control his Oni powers, Asumu later inherits the power to become Kamen Rider Hibiki, and uses his new abilities to work together with Akira and Todoroki to ally their schools. Asumu later appears in the World of the Rider War after his reality is absorbed into it, being the only survivor of the attack of the Fangires led by Kamen Rider Saga thanks to Daiki. After defeating Super Apollo Geist, the convergence of worlds is not stopped and the World of Hibiki and Asumu disappear. Following Decade's death, he is revived and reunited with his friends. He later helps revive Decade and then appears along with Wataru to aid Decade in the final battle with Super Shocker to repay Decade for saving his world, turning into Armed Hibiki thanks to Decade's K-Touch.
Ibuki / Kamen Rider Ibuki
Ibuki has the ability to transform into Kamen Rider Ibuki who is master of the trumpet-based Ongekido Ibuki Style, running the Ibuki Lesson Studio. He and his entirely female student body wear uwagi with hakama; Ibuki has kataginu on top of the uwagi. After listening to Akira's reasoning and Tsukasa's advice, he discards his rivalry with Zanki and steps down as teacher in favor of Akira. He later fights without his "mask" against the Bakegani, wielding a trombone version of the Ongekidan Reppu.
Akira / Kamen Rider Amaki
Akira is Ibuki's head apprentice who has the ability to transform into Kamen Rider Amaki, who visually resembles Ibuki. During Gyuki's rampage, she transforms and fights alongside Todoroki in order to save Asumu, all without Ibuki's permission. Braving his displeasure later, she and Todoroki convince Ibuki and Zanki that allying the three schools would be the best thing for the future of Ongekido. With Tsukasa's help, they convince their masters, and she is promoted from apprentice to teacher. Akira later appears in the World of the Rider War after her reality is absorbed into it, killed by Kamen Rider Saga. However, when Decade is killed by Kivara, the World of Hibiki is restored along with Akira and Todoroki.
Zanki / Kamen Rider Zanki
Zanki has the ability to transform into Kamen Rider Zanki who is master of the guitar-based Ongekido Zanki Style, stationed at a dojo. He is Ibuki's rival and thus their schools are sworn enemies. Zanki and his entirely male student body wear karate gi; Zanki's gi is black and he wears a black haori over it. After being convinced by his student to give the idea of allying the three schools a chance, he steps down as mentor in favor of Todoroki. He later joins the fight without his "mask" against the Bakegani, wielding his Retsuzan.
Todoroki / Kamen Rider Todoroki
Todoroki is Zanki's head apprentice who has the ability to transform into Kamen Rider Todoroki. Though a member of Zanki's school, he has feelings for Akira, and sides with her and Asumu when discussing how important allying the three schools is to the future of Ongekido. Zanki isn't pleased by such an idea, but with the help of Tsukasa and Akira, he manages to convince his master, and he is allowed to move from an apprentice role to teaching. Todoroki later appears in the World of the Rider War after his reality is absorbed into it, killed off while attacked by Fangires under Saga.]But once Decade is killed, Todoroki and Akira are restored along with their world.
Kamen Rider Ohja
Takeshi Asakura is a sadistic criminal who transformed into Kamen Rider Ohja. In Decade, Ouja is summoned in the World of Hibiki by Kiva-la, wielding a kanabo which he uses to summon a Bakegani from the mountain side after knocking Kiva-la aside. Asakura later appears in the World of Decade to prevent Dai-Shocker from taking over, but soon defects to the side of Dai-Shocker.
The Makamou are an assortment of monstrous creatures that usually dwell in the rural areas of Japan and consume any human beings as food. There are two main variations of this group: the bestial Giant Type and the humanoid Summer Type. In the first episode, Makamou such as the Bakegani and Ooari attack Natsumi while others like the Ubume were involved in the all-out battle among the monster groups that destroys the world.

Hibiki / Gyuki
Hibiki is the master of the taiko-based Ongekido Hibiki Style. 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 must slay his former master as his final request.
In Episode 18, a Summer Type snapping turtle/frog Makamou, it was first one that Tsukasa and company encounter before Asumu arrives to fight it. In the end, the Kappa is destroyed by Decade using Kabuto's Rider Kick.
In Episode 18, a trio of Summer Type cat Makamou. While the first two are destroyed by Zanki and Ibuki, the last one evades them before being destroyed by Decade's Dimension Kick.
In Episode 18, a Summer Type ape/parrot Makamou that attacked Hibiki and Asumu, overpowering Kuuga until Hibiki assumes his Oni form and destroys the Makamou.
In Episode 19, a Giant Type swimming crab Makamou, larger than the average type with more pincers. It is released by Takeshi Asakura and appears with Narutaki riding on it once Gyuki is destroyed. The Bakegani is destroyed through the combined efforts of Hibiki, Decade, Diend, Amaki, Todoroki, Ibuki, and Zanki.
Series:  Kamen Rider Decade