AB-Type-kun possesses a capricious and unpredictable nature, blending the stereotypical traits of both A and B blood types. This dualistic personality leads him to act with rational calculation in some moments and appear eccentric or emotionally detached in others. His interactions within the group consistently offer a unique perspective that stands apart from the others.

As part of a narrative built on anthropomorphized blood types, his character explores common cultural stereotypes through exaggerated behavior. The humor and dynamics of the series stem from these portrayals, with AB-Type-kun embodying the perceived complexities and contradictions of his type.

The anime's second season introduced female counterparts for the main characters, including a female AB type. These additions expanded the scope of group interactions and situational comedy, providing new contexts to observe the stereotypical behaviors of all blood types.