Kai Shimada is a supporting character in the anime, depicted as a towering and muscular man who is a member of the Shinesengumi. His physical appearance is notable for his large stature and a design that often includes a sword and coat, with no visible hair on his head. As a figure associated with this group, his background is tied to a historical context of combat, as it is said that until his death, he participated in the majority of battles with the Shinsengumi.

His personality includes a pronounced weakness for sweet foods, which contrasts with his formidable and imposing physical presence. This combination of a giant warrior with a gentle sweet tooth informs his demeanor and interactions. Within the story, his role is secondary, serving as a member of the Shinesengumi and interacting with the main character and other figures in the narrative. His specific motivations stem from his past life as a warrior, and his actions in the series are consistent with that experience.

Key relationships are primarily defined by his association with the Shinesengumi, though specific ties to other named characters are not extensively detailed. His development throughout the series involves the juxtaposition of his past as a fierce warrior and his present state, but detailed arcs of personal change are not a primary focus. His notable abilities are rooted in his combat experience from his lifetime, making him a capable fighter with a sword.