The universal theme of friendship, in all its vulnerability, tenderness, and purity, is explored in this drama. The flow of seasons forms a thematic continuity to the action: the severity of youth in summer, the sentimentality of autumn, and the frustration of winter. Together, this group of boys cope with common adversity, face the death of a friend, and prepare to deal with the world of adulthood.

Shiratori Sakuto is 28, but has the intelligence of a 6-year-old boy. He works for Dream Flower Service, a flower distribution centre which provides employment for problem youth. One day, he and a colleague, Yanagawa Ryuichi, delivers a rose bouquet to the apartment building where Mochizuki Haruka lives. Because Haruka does not know that the deliveryman is mentally challenged, she is shocked by his response and tries to call the police. Haruka works for a brain physiology research centre where Professor Hachisuka Daigo has been studying the improvement of mental performance. He has succeeded in lab experiments on a white mouse called Algernon. Sakuto is transformed into a genius through surgery. But Algernon's new intelligence begins to fade, and he dies. Sakuto realises that his genius, too, is destined to leave him.

Brought on by popularity for the series, this DVD Special feats. two half-hour side stories that take place during the events of the show. Both stories appear to take place just after episode 20, the first episode of the Helheim Saga. The Kamen Rider Zangetsu side story begins with Takatora telling Kota about the truth behind Helheim. While a childhood friend pays Takatora a visit, a mysterious Kamen Rider that has control over cracks begins to hunt down Yggdrasill’s forces. The Kamen Rider Baron side story begins with Kaito seeking out the Overlords for Professor Ryoma. A prince visits Zawame and when he finds out that Kaito looks exactly like him, he decides to forcefully switch lives, resulting in conflict.