Hyakutarō Onigawara is a second-year high school student in Group K who participated in the "Friendship Hide-And-Seek" game, managing the food station with Chisato Hashiratani. Initially presenting as rude, impulsive, and easily angered—particularly toward authority figures like the basketball club captain or during interactions with females—he masks a deeply passionate core. His explosive exterior contrasts with sensitivity about past mistakes and persistent assertiveness. Chisato Hashiratani identifies him as a "tsundere," noting how he buries genuine concern beneath aggression. For example, he intimidated Kei Shinomiya to block his basketball club entry, intending not malice but protection from the team’s grueling regimen. His background centers on the high school basketball club. A pivotal incident saw his inaccurate shooting injure captain Juuzou Kadokura, an event that profoundly impacted him. This drove Hyakutarō to relentless practice, aiming to support the captain’s final sports opportunity. Juuzou Kadokura acknowledged Hyakutarō and Chisato as Group K’s fastest runners. However, Hyakutarō’s movements were highly predictable, limiting his effectiveness in physical confrontations. He displays marked naivety and deference around women, influenced by his grandmother’s advice to "be nice to females." This surfaces in unusually polite behavior toward Maria Mizuse. He also struggles with morning alertness and prefers coffee heavily adjusted with milk and sugar.