The Cast Showoff: C'mon, it's Akira Fuse. He can't show his vocal songs for nothing.
Cast the Runner-Up: The character of Akira was created in response to Eri Akiyama’s audition being strong enough to net her a part of her own.
Executive Meddling: One of the most infamous examples in the history of Kamen Rider. As the toys of Hibiki were selling poorly, the higher ups blamed the show for this, giving it a drastic retool around episode 30, in an attempt to make it more 'Kamen Rider-like'. To list a few examples of the effects of this retool:
Kiriya Kyosuke was introduced to give Asumu a rival.
Asumu is no longer the focus of the show, giving more screen time to the Oni Riders. Each of them also gets a story arc of their own.
The overall tone of the series is changed from a slice of life series with supernatural elements, to a more action oriented superhero show.
Although it is worth noting that Hibiki's actor swore never to come back as a result of the aforementioned Executive Meddling the show went through, he later clarifed he would be happy to come back as long as Shinichiro Shirakura was not involved.
Although there's probably a few examples listed above that wouldn't have happened if it wasn't for Executive Meddling, one other example stands out: the entire series was based on Onigeki Hibiki, a story by Shotaro Ishinomori. Suppose that instead of deciding to adapt said story into a Kamen Rider series, Toei had created a new Kamen Rider series - what could we have gotten instead?
Both Asumu and Kiriya were originally supposed to become Oni by the finale of the show, but Asumu's suit was scrapped to enhance the look of Kiriya's suit. We get an idea of what might have happened in Kamen Rider Decade's "World of Hibiki" arc, however, where the counterpart of Asumu ends up becoming Hibiki after the original in that world dies.
According to the Winter 2012 edition of Toei Hero MAX, the first producer Shigenori Takadera offered a writing position to Yoshio Urasawa at one point, having worked with him on Gekisou Sentai Carranger previously. Urasawa’s writing was ultimately deemed too heavy on his preferred gag comedy style to match the tone Hibiki was going for.
Other trivia
Accounting for SIC Hero Saga stories, Habataki is currently the only movie Rider in the entire Kamen Rider franchise to have a Legend Rider device (barring KamenRide cards) that a Rider properly transforms withnote Eternal has his own Ridewatch, but this is never brought up in the show proper or related material, with a counterpart of Eiji Hino uses a modified Taka medal based on Habataki (along with a Tora medal based on Tiger and a Batta medal based on Ichigo) to inherit their powers and transform into Legend Tatoba.
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