Shoma, who comes from a different world, is saved by a boy named Hajime when he collapses from hunger. Shoma excitedly eats the snacks that Hajime gave him, but as soon as he does, Gochizo are born one after another. Meanwhile, freelance writer Hanto is gathering information on the appearance of "monsters" while doing research. Hajime hides Shoma in his secret base and hurries home when a mysterious man appears before him. The man transforms into the monster Granute and approaches Hajime. Shoma tries to save Hajime, but he is no match for the Granute. Gochizo suddenly appear in front of the suffering Shoma. Shoma sets and eats the Gochizo! He transforms into Kamen Rider Gavv and confronts the Granute!

Shoma, who has collapsed from hunger again, is helped by Sachika, who runs an anything and everything general store, and treats him to lunch and snacks. Hanto, while working on a case story, discovers information about Gavv on a social networking service. He starts interviewing witnesses. Shoma is asked by Sachika's friend Ritsu to assist her in her "anything goes" job. That night, Shoma is led out by a Gochizo, who suddenly appears, and runs into a man dressed in a jogging outfit. The man transforms into a Granute, and Shoma transforms into Gavv, and they clash!

By chance, Shoma meets a tough-looking man named Sujimoto and decides to help him with his work as he is asked. Then Sujimoto is attacked by a Granute. Shoma receives a call from the Gochizo and rushes to the scene, where he transforms into Gavv and challenges the Granute to a fight. The Kamen Rider appears! Hanto receives the news from Sachika and witnesses Gavv's battle...!?

Shoma mistakes the vegetables in the field for wildflowers and is caught by the owners of the field, Ryoji and his wife Mutsuko. After the misunderstanding is cleared up, Shoma is welcomed kindly by the couple. Hanto visits Granute researcher Suga and begins researching the Granutes. When Hanto is told about the true nature of Granutes, who kidnap humans to spice up sweets, he...!? An agent appears in front of Shoma, who is spending time with an elderly couple. Shoma escapes and confronts the agent, but then an unexpected person appears...!

Shoma collapsed from hunger and was saved by a mysterious monster. Is it a new Granute? Shoma wakes up and transforms into Gavv, but his movement was halted by an unexpected reaction: "The surgery was a success!" Who is this monster? After receiving a report from the Gochizo, Shoma once again confronts the Agents. He transforms into Gavv and clashes with the two Agents. Hanto, who was watching the scene, is rescued and desperately pleads with those who fear Gavv's appearance, "He's not a monster!" He desperately appeals to the people who are afraid of Gavv's appearance, but...

Shoma starts a new life at Sachika's "Happipare". Meanwhile, Suga has succeeded in developing an item that can transform a person into a Kamen Rider, and asks Hanto to try it out. A new Granute appears. Shoma transforms into Gavv and fights to his advantage, but the Granute counterattacks and escapes. Hanto stood in front of the Granute and transforms into Kamen Rider Valen with an item developed by Suga...!

Gavv confronts Valen, the new Kamen Rider who defeated the Granute. Unaware of each other's true identities, the two begin to probe each other. Later, Sachika and Shoma are asked to do housework at a relative's mansion, where they meet a young artist who lives there. Meanwhile, Hanto visits a gallery to investigate an unsolved disappearance...

When Shoma asks Sachika why she is covered in paint, Sachika simply says that she made a mistake. Sachika, who does everything so dexterously, only replies that it was her own mistake. Shoma senses that there is a deeper reason, and bites his lip because he is helpless to help Sachika. A new art dealer comes to Masako's mansion to see the studio of Suetsugu, an aspiring painter. Suetsugu also gets a scout! Hanto is suspicious that the art dealer might be a Granute. He has to be sure.... Then Shoma comes up with a plan...!

Shoma gets candy from children dressed in Halloween costumes. He is thrilled to taste the first candy that does not melt immediately, and new Gochizo are born one after another. Meanwhile, Hanto approaches Kirari and her friends, who gossip about monsters. He goes to Kirari's dance school to look for clues. Then he sees a suspicious man following Kirari's friend Rika...!

Hanto comes to "Hapipare" to ask for help in finding a missing cake store. Shoma hears about it and secretly sends the Gochizo to search for it. The Gochizo's report reveals that the owner of the suspicious cake store is at the kindergarten. Shoma and Hanto sneak into the kindergarten and find that the owner is actually a Granute! Hanto escapes Shoma, transforms into Valen, and angrily attacks the Granute. Gavv joins him, and the two join forces to confront the Granute...!

Hanto has become a "suspect" in a romance scam. Called by Shoma and Sachika, Hanto goes to the coffee shop where he is supposed to meet a woman in order to catch the real culprit. Shoma, in pursuit of the Granute, tries to transform into Gavv, but then Lango appears. Shoma is alarmed by their unexpected reunion, but what are Lango's intentions...!? Meanwhile, Hanto also discovers the Granute. He transforms into Valen and fights, but he has a hard time and is finally hit by a powerful blow...!?

Hanto, who was rescued by Gavv, presses Gavv to reveal his true identity, saying it's not fair. Gavv is perplexed, but he has no choice but to release his transformation...! Sachika discovers a man on social media who she believes may have deceived Emi. Shoma goes to meet the man with the information and runs into a Granute. "I'm going to beat you today!" Shoma says as he transforms together with Hanto!