Seishirou Kikumasamune, son of a prominent hospital director, hails from an affluent background. He commands respect as the Student Body President at prestigious St. President high school, recognized for his exceptional intellect and leadership. His academic prowess spans multiple disciplines, excelling notably in pharmacy, languages, and occult studies. He actively participates in various school clubs, including the UFO Research Society.

Physically adept, he masters Kempo martial arts and demonstrates superior combat skills compared to peers. This fighting ability is enhanced by sharp observational skills, allowing him to swiftly identify weaknesses in others. Despite his capabilities, his demeanor remains reserved, occasionally lacking overt kindness and manifesting as teasing toward close acquaintances.

Within the group dynamic, he functions as the primary strategist, devising plans to resolve mysteries or conflicts. This role involves close collaboration with the vice president, especially during high-stakes situations. He exhibits a protective instinct, particularly toward childhood friend Noriko Hakushika. This protectiveness occasionally drives elaborate group efforts aimed at ensuring her happiness. Unspoken emotional layers within his complex feelings for Noriko influence his actions.

His personal style frequently incorporates traditional elements like kimonos or patterned sweaters, projecting a mature appearance beyond his years. He attracts considerable attention from gay men. While initially presenting as emotionally detached, his involvement in group activities and problem-solving scenarios gradually reveals deeper engagement with his peers over time. His portrayal across adaptations remains consistent in these core traits and responsibilities.