O-Type personifies the O blood group, one of four central characters embodying Japanese and Korean cultural stereotypes associated with blood types. His characterization consistently reflects documented O-type traits across all media appearances, including television episodes and special releases.

Fundamentally laid-back, easy-going, and friendly, he displays a kind-hearted nature. He exhibits confidence, self-determination, and strong leadership tendencies, often emerging as the de facto leader in group dynamics. His leadership manifests through diffusing tense situations and fostering cohesion among the blood types. He demonstrates creative problem-solving and adaptability in scenarios ranging from everyday social interactions to shopping, training camps, work environments, and mixers.

Despite his generally relaxed demeanor, he occasionally displays stereotypical negative traits like impulsiveness, unpredictability, and self-centeredness, particularly in situations requiring quick decisions where consequences may be overlooked. His interactions reveal competitiveness, athleticism, and a capacity for both agreeableness and stubbornness.

The character operates within a fixed framework defined by blood type personality theory. His traits and behaviors remain strictly consistent throughout all official media, adhering to the established O-type archetype. His role primarily illustrates and humorously explores the purported characteristics of the O blood type through situational interactions with the other characters.