Motoharu Kaidō is a student at BABEL, the international organization that trains and protects young people who have returned from the alternate world of Alayzard. He is a member of Class A, the elite group of students, though he considers himself an underachiever among them. Despite his well-groomed appearance, he frequently claims to be poor. He has short blonde hair and brown eyes.

Kaidō is cheerful and often acts as the class clown, earning the reputation of the eternal clown of Class A. He is known to be clumsy and lighthearted, frequently greeting the protagonist Akatsuki Ousawa with an aggressive handshake that replaces a punch. He enthusiastically declares himself Akatsuki's best friend and calls him Akkii. Beneath his jovial exterior, however, he has a more mysterious and calculating side, and he is implied to have ulterior motives. He is secretly a member of an organization called Crimson Twilight, and he has the rare experience of having traveled to another world twice.

His role in the story is that of a supporting character who provides comic relief while also acting as a key link to deeper conspiracies. He introduces Akatsuki to Sleipnir, a vehicle once used by Akatsuki's father, the founder of Crimson Twilight. After the events involving the character Phil, Kaidō accompanies Akatsuki and Miu on their journey back to Alayzard.

Kaidō is fast and appears to use a fighting style similar to Akatsuki's, which involves quick, kick-based attacks. The full extent of his powers remains unknown, and he has so far refrained from directly confronting Akatsuki, suggesting that he is waiting for the right moment or holds hidden strength. His abilities and true intentions are not fully revealed during the anime adaptation.