Doronpa is an American ghost who arrives in Q-Taro's town, instantly becoming his rival and occasional friend through mischief and boasts of American ghostly superiority. He claims this intellectual edge to provoke Q-Taro and win admiration. His rivalry deepens due to his attraction to U-ko, Q-Taro's girlfriend, who admires Doronpa's smarts and often assigns Q-Taro chores or judo practice. Doronpa actively courts U-ko's attention, using her respect to further annoy Q-Taro. He also harbors feelings for P-ko, Q-Taro's younger sister, complicating their conflict.

A key trait is Doronpa's exploitation of Q-Taro's fear of dogs; he transforms into a canine specifically to frighten him, a frequent tactic in confrontations that serves as both a strategic advantage and comedic antagonism.

Despite their clashes, Doronpa shows sporadic camaraderie with Q-Taro and the humans. He lives with Kaminari, the Ohara family's neighbor, integrating into the community while remaining an agitator. In a significant deception, Doronpa impersonates Q-Taro during the latter's brief absence in the ghost world, trying to convince everyone Q-Taro never left. This scheme unravels upon Q-Taro's return, restoring their usual dynamic.

Doronpa's personality blends boastfulness about his American origins with playful troublemaking. He consistently acts as Q-Taro's foil within group antics, teasing him about cultural differences and romantic competition, especially concerning U-ko and P-ko.