|This article is about a/an alternate reality/A.R. World (another rider's world) in Kamen Rider Decade.|
The World of Hibiki (響鬼の世界 Hibiki no Sekai) is the alternate reality where a version of Kamen Rider Hibiki takes place. In this world, humans train to become Oni within one of three rival schools of sound-based martial arts called Ongekidō (音撃道 Ongekidō, "Sound Attack Way"), all based on different interpretations of the writings of the Grand Master (大師匠 Daishishō), the creator of Ongekidō.
The masters and students of the Ongekidō styles wear traditional Japanese clothing, Tsukasa donning such attire while in the A.R. World and given the ability to use the Ongekibou. Daiki's treasures in this world are the three scrolls containing the secrets of the three schools of Ongekidō. The backdrop used to enter this world depicts a forest with a taiko drum in the foreground.
Nearly all of the original cast of Hibiki returns to reprise their roles, with only Shigeki Hosokawa (the original Hibiki) and Rakuto Tochihara (the original Asumu) absent. The episodes also show calligraphic representations of the Kamen Riders' names: "Tsukasa Kadoya" (門矢 士 Kadoya Tsukasa), "Photo" (写 Utsushi), "passing through" (通 tooru), "Decade" (ディケイド Dikeido), "Sea Cucumber" (海鼠 Namako), and Pink (桃色 Momoiro) for Decade; "Clear-Self" (空我 Kūga) for Kuuga; "Peach" (桃 Momo) for Momotaros; and "Thief" (盗 Tō) and "Diend" (ディエンド Diendo) for Diend.
Arriving in the last world, the World of Hibiki, Tsukasa and company began the search for Kamen Rider Hibiki when they are ambushed by the Makamou Kappa. An Oni in training named Asumu battled the monster until Decade used Kabuto's powers to destroy it. On learning he was Hibiki's pupil, Tsukasa had Asumu bring him to his mentor. Upon seeing Tsukasa, Hibiki, who was shirking off from his duties as an Oni, believed him to be the legendary Ongekidō Grand Master. Meanwhile, Zanki slays a band of Bakeneko as Ibuki arrived to take them out as well. But when the last Bakeneko escaped them, Decade destroyed it with the two groups as witness. Tsukasa visited Ibuki's school afterwads and talked with Ibuki and Akira about three special scrolls. Meanwhile, after failing to rob Hibiki as he took his leave, Daiki was forced into becoming Asumu's mentor. Like Tsukasa, Daiki learned of the three scrolls of the Oni classes, and he convinced Asumu to become Hibiki's pupil again, before taking his leave to Zanki's dojo where he offered a proposition. Returning to find Hibiki and Asumu attacked by a Tengu, Kuuga attempted to battle the Makamou. At the same time, Natsumi encountered Narutaki as he revealed Tsukasa's actions actually doomed the worlds rather than saved them. When Kuuga was nearly killed, Hibiki assumed his Oni form to destroy the Tengu before he suddenly transformed into the monstrous Gyuki. While this occurs, the Ibuki School and Tsukasa receive a challenge from Zanki's School and Daiki with the scrolls on the line. With them representing the two Oni schools, Decade and Diend did battle. But once Diend revealed his intentions to steal both scrolls, he summoned Momotaros who attacked the Oni Kamen Riders until Gyuki stormed in and overwhelmed the Oni. The episode ended with Decade using Ryuki's powers to take on the Makamou.
Using Ryuki's powers, Decade battled Gyuki while Ibuki and Zanki argue whose fault this was. When Akira and Todoroki joined the fray in their Oni forms to save Asumu as he tried to protect them, with Decade joining them by using Den-O's Ax Form, they managed to defeat Gyuki. He ran off before regressing to Hibiki, and Yusuke and Natsumi found him shortly after. Later that night, after talking to Asumu, Akira and Todoroki confronted their mentors to put aside their differences, with Tsukasa supporting them. Ibuki and Zanki promoted them to the role of new teachers of their respective schools. Meanwhile, Hibiki revealed the nature of Gyuki to Yusuke and Natsumi as Daiki arrived to claim the last scroll. Hibiki stopped him and gave Daiki his Onsa to give to Asumu with a final request. The next day, after suffering a Narutaki-induced vision of the future resulting from their actions, Natsumi found Daiki, who used Asumu as his cover to steal the final scroll. But as Tsukasa arrived, Daiki evoked Hibiki's final change into Gyuki to Asumu's horror, and the thief left them. After learning the secret of the three scrolls to be all schools as one, Daiki returned to give Asumu the Onsa. Asumu became Kamen Rider Hibiki in order to honor his mentor's final request: slay the Makamou to free Hibiki's soul. However, Narutaki arrived on a giant Bakegani (summoned with the help of Kamen Rider Ouja), with Todoroki and Amaki showing up shortly after. Once Diend destroyed the scrolls, revealing that the true Ongekidō was all three styles in harmony, Decade regained Hibiki's powers. Decade, Diend, and the Oni all finished the Makamou off together. After Asumu and company thanked Daiki for uniting the schools, Tsukasa and company returned to Natsumi's world with Natsumi a bit worried.
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 Apollogeist, 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 Akira and Todoroki. 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 and later into his Hibiki Ongekiko form with the All Rider Final Form Ride Card to fight the Super Crisis Fortress.
In the novel reimagination of the Kamen Rider Decade TV series, Kamen Rider Decade: The World of Tsukasa Kadoya ~The Garden Inside the Lens~, the World of Hibiki is, as one of the Nine Worlds, not an alternate reality like in the TV series but the original world. The World of Hibiki is one of the six worlds the Hikari Studio group, Tsukasa/Decade, Kaito/Diend, and Natsumi, have already traveled to by the start of the novel as they head for the three remaining worlds, and thus not much is seen about it.