Shoma is a young man who came from another world. Shoma meets a boy and is excited to see the world for the first time. Meanwhile, the crisis of the monster Granut from another world approaches. They were secretly attacking happy people in order to obtain "dark sweets." After eating the sweets, Shoma awakens his powers and stands up against Granut's threat with his follower Gochizou. ``Protect the people you care about with the power of your favorite sweets'' Shoma's determination sets the story of ``Kamen Rider Gav'' into motion!

It's been a week since Shoma came to the human world. Shoma collapses from hunger and is picked up by a woman. Her name is Yukika Amane. The gal president of the all-purpose shop ``Hapipare.'' In order to repay Yukika, Shoma decides to help Happipare with his work. Behind the scenes of Shoma's struggle with his first job at Happipare, dark clouds are gathering in the world of granules. Stomach is a major confectionery company in the granule world. The Stomach family, led by company president Rango Stomach, was pursuing a certain person who enriched their own pockets by manufacturing dark sweets. The peaceful daily life is short-lived, but once again Granut appears, targeting happy humans, and Shoma is once again thrown into battle...

Shoma rescued Yukika's friend from Granut. However, he is feared as a monster and decides to leave Yukika in order to hide his true identity. While searching for his next new home, Shoma is picked up by a timid old man. Granut's evil hand approaches Shoma, who is acting with an uncle who seems to be acting strangely. Meanwhile, Kizunato, who is looking for his mother's enemy, continues his own investigation and ends up asking an unexpected person. Shoma and Kizuna. As the wheels begin to move, the fates of the two men gradually become intertwined.

After saving the scary old man with soda punch, Shoma is left alone again. A lonely Shoma is picked up by a kind-hearted elderly couple on a remote country road. They spend some happy time with an elderly couple who love Shoma, who is exactly like their lost son, like his own son. However, as Kamen Rider's existence gradually comes to light, Sheeta and Jeep become aware of Shoma's survival, and the two finally confront each other...! With the power of marshmallow, Shoma faces off against a strong enemy!

Shoma successfully defeats Sheeta and Jeep's agents and saves the elderly couple. However, fearing that the happy people around him may be in danger, he decides to cut off all contact with people. The orphaned Shoma is picked up by a giant Granut deep in the mountains. His true identity is Shoma's great-uncle, Dente Stomach. He left the Granite World and retired to the Human World. Shoma is told an unexpected truth by Dente and has to face his painful past. Meanwhile, even as Kizuna approaches Kamen Rider, the threat of Granut approaches...!

Shoma hears about his past from his great uncle Dente. After much conflict, he begins to move with determination to protect humans from Granut's evil deeds. Shoma moved from place to place for a while, but decided to return to Yukika and work for the happiness of people. Meanwhile, unbeknownst to Shoma, Kizuna is in a big crisis. Kizuna's writer master, Shioya, is targeted by Granut. Kizunato, fighting against his cruel fate, is forced to make the decision to become a Kamen Rider.

Kizuna undergoes biological modification at the hands of Granut researcher Suka, and transforms into Kamen Rider Valen. He vows revenge on Granut, who took not only his mother's life but also his master's life, and begins to take action with the aim of annihilating Granute. Valen ends up meeting Gav for the first time without knowing each other's true identities. Meanwhile, Shoma and Yukika visit the atelier where aspiring artists live at the request of Yukika's great-aunt Masako. So, in order to protect the artist's egg from Granut's evil hands, Gav uses the power of chocolate Gochizou to fight back!

Grotta, the eldest daughter of the Stomach family, suddenly appears in the human world. Valen is forced into a corner before Grotta's overwhelming power! Rango, the eldest son of the Stomack family, hears of the existence of Kamen Rider hunting Granut, and a family meeting is held where the five members gather. Meanwhile, Shoma defeats Granut, who is disguised as a patron, and saves Tamaki, a three-dimensional modeling artist. However, Granut, who was supposed to have been defeated, is targeting the aspiring artist again, and a crisis approaches Takarayashiki Low. Gav is Valen, and the two decide to fight together for the first time with the power of Chocogochizou! A chocolate-covered tag team match begins!

Gav and Valen worked together to save the artist's egg from Granut. The crisis at the Takarayashiki mansion has been overcome, and one job has settled down. Following the fall of art, “Halloween” is coming! Halloween is a dream come true for Shoma, where he can get lots of candy if he dresses up. Granut begins to move, aiming for such a happy Halloween mood. Meanwhile, Kizunato meets Kirari, a girl who attends a dance class, and hears rumors about a series of missing people. Theta and Jeep, who were fired from Stomach, are also working behind the scenes, threatening the happy Halloween!

Kizunato follows the shadow of Granut, who is targeting children. They arrive at a cake shop based on the clues Granute dropped, but not only Granute, but the entire shop has disappeared. Meanwhile, Granut's evil hand approaches Kirari, a girl who has deepened a friendship with Kizunato. Shoma defeats Theta Jeep's strategy with the power of candy, and together with Kizunato, he ends up pursuing the mystery of the missing cake shop. Will the two who hide the fact that they are both Kamen Riders be able to save Kirari? ?

Gav and Valen defeat Granut, who is targeting children. By chance, Shoma meets a pair of beautiful sisters for some reason. Emi, the older sister, falls in love with a man she met online, and Hana, the younger sister, suspects that he is a romance scam. Shoma tries to help the two who are in trouble and takes them to Happipare. When Eimi listens to the story, it turns out that the person she fell in love with was an amazing person. Shoma and Yukika take action to find out the truth behind this impossible situation. Meanwhile, Rango, who has given up on Sheeta and Jeep, who have been making many mistakes, finally begins to make a move on his own. Rango's destination was the human world.

Valen collapses under Granut's fierce blow. Shoma witnesses for the first time that Valen's true identity is Kizunato. Although their circumstances are different, Shoma and Kizuna have similar pasts. Their thoughts intersect for the first time, and the story begins to take a big turn. Meanwhile, Yukika struggles to find out who is committing the romance scam. Shoma carries out a certain strategy and decides to lure Granut, the culprit. Rango, who has returned to the Granut World, thinks that Gav could become a threat due to Shoma's growth, and starts a new plan.

Shoma and Kizuna discover that each other's true identities are Kamen Riders. However, Shoma was unable to confide in Kizunato, who had a grudge against Granut, that he was also Granut. At that time, Sheeta and Jeep, who were fired from the Stomach company due to their failures, are kicked out of their base and end up getting lost on an outcrop. All of his anger is directed at Shoma, and he sets out to eliminate Gav with his own hands. Unaware of this dangerous situation, Shoma decides to make a Christmas cake with Yukika. For Shoma, cake was something that had a special meaning.

Shoma faces a direct confrontation with Sheeta and Jeep. Gav counters with the power of Bush de Noel, but is defeated by the overwhelming power of the two angry men. Having missed the final blow, Sheeta and Jeep carry out a strategy involving innocent people to lure Shoma. Meanwhile, Yukika, who had promised to eat cake together, continues to wait for Shoma to return. Will Shoma be able to return to Yukika and fulfill his promise? Next time, Gav's mighty power will awaken! Shoma VS Theta Jeep, the fateful sibling battle is finally settled! ?