Season 1

Long ago, the Twelve Animal Signs formed the Zyunishi Doumei (The Twelve Animal Signs Alliance) to protect humanity from mysterious lifeforms known as FUKASHIGI. Preparing for an inevitable battle against FUKASHIGI, the members of the Zyunishi Doumei entered a 100-year slumber. In the present day, Sora Otosumi serves as the personal Meister of the Mizuki family. To protect the family's daughter, Yuna Mizuki, he transforms into Kamen Rider MY-TH and joins the fight against FUKASHIGI. But when Sora comes into conflict with the Twelve Animal Signs over FUKASHIGI, a new Kamen Rider “myth” begins!

As Tatsuomi, who had infiltrated the Mizuki household as a tutor, continued his investigation, a new Fukashigi emerged. Sora transforms into My-Th, but just then, Datt appears. Datt transforms into Kamen Rider Datt and, ignoring the astonished My-Th, launches an attack on the Fukashigi. Datt uses her exceptional jumping ability to corner the Fukashigi, but My-Th intervenes, turning it into a three-way battle...!?

Yuna meets Shiori, a girl whose father has gone missing in the city, and deduces that it’s the work of a Fukashigi. Sora also begins his own investigation. Tatsuomi, who had been keeping an eye on Sora, witnesses Sora transform into My-Th right in front of the Fukashigi. Seizing the moment, he pulls out his own Driver and transforms into Kamen Rider...!

In order to bring Shiori’s father back, Sora and Yuna are working tirelessly to combat the Fukashigi. After discovering a clue, Sora asks Tatsuomi for help. The Fukashigi reappears. Sora transforms into My-Th, but once again, Rid interrupts. My-Th shifts into Wolf Frame and, keeping an eye on Rid, corners the Fukashigi—but...!?

Tatsuomi is suspicious of Sora, who is unusually open about his emotions. Just then, Yuna sends them new Fukashigi information. Sora transforms into My-Th and challenges the Fukashigi, but Jyao, who is after My-Th’s transformation device, intervenes...!

After analyzing the Fukashigi that had fled, Sora left Yuna, who was complaining of feeling unwell, behind and set off in pursuit of it alongside Tatsuomi. When Sora transforms into My-Th in front of the Fukashigi, Jyao appears once again. As Jyao relentlessly targets My-Th, Vanken intervenes, shouting, “You’ve got the wrong person!” but...!

An unprecedentedly powerful Fukashigi appears, and My-Th finds even his finishing move blocked. He must defeat the Fukashigi for Yuna’s sake... Sora challenges the Fukashigi, which has reappeared. Furious at My-Th’s actions, Mutn lunges at him. Right in front of a worried Tatsuomi, Mutn transforms into a Kamen Rider. As the battle intensifies, a new enemy even appears...!?

My-Th suffers a crushing defeat at the hands of Maou, with no way to fight back. Sora is left on the brink of death. Tatsuomi asks Yuna, who is staying by Sora's side, why Sora started fighting in the first place. Having tasted the fear of death from Maou's attack, Sora can no longer fight... Tatsuomi heads to the scene where the Fukashigi appeared to take Sora's place. However, he is ambushed by the Fukashigi and is instantly cornered...!?

No overview available for this episode.