Kamen Rider Hibiki and The Seven Senki

Hibiki and Asumu are on their way to a Makamou attack on the beach. Once they arrive there, they see dozens of people running from the massive Orochi, a beast rumored to be the strongest Makamou ever created. Once they arrive, Hibiki walks towards the Orochi and transforms, but all of his attacks prove useless against Orochi. The situation is made even more dire when Hibiki jumps in the way of an attack meant for Asumu. Taking the full force of the attack, Hibiki passes out as the Orochi swims away, leaving a panicking Asumu to get help. Hibiki ends up in the hospital and Asumu begins blaming himself for Hibiki's injuries. Feeling useless, he begins helping at Tachibana's, going through dozens of books to try and discover a way to defeat the Orochi. Upon coming across a book with his name on it, Asumu sits down and begins to read what turns out to be the history of Takeshi, the Oni and the Makamou war.