Kōji Dōshita serves as an initial blacksuits member on Team Tonegawa, subordinate to Yukio Tonegawa within the Teiai Group. At 32, his background as a rugby team captain at T-Kyo University profoundly shapes his teamwork and leadership style. His sports-minded, hotblooded nature drives him to actively encourage colleagues facing challenges, notably motivating Heihachi Gonda during Gonda's temporary leadership while Tonegawa is ill.

Dōshita exhibits intense discipline regarding health and fitness. During Tonegawa's medical checkup, he imposes rigorous dietary control, discarding high-calorie meals like lunch boxes to ensure compliance, an approach Tonegawa describes as making him feel "like a man under surveillance." This strictness extends to his personal habits, as seen when he consumes unconventional foods such as grasshopper tsukudani and frog sausages without hesitation.

He has a younger brother, Takashi, who is notably petite and works part-time assisting Team Tonegawa, offering minor insight into Dōshita's background.

After the Restricted Rock-Paper-Scissors project concludes, Dōshita returns to the Teiai Group's public relations department. There, he channels his athletic passion into establishing a rugby club, leading the team to victory in a tournament, highlighting his return to a sports-oriented environment and suggesting a positive professional resolution.

Throughout the series, Dōshita actively participates in Team Tonegawa's efforts to design and execute the death game. While his individual contributions are less prominent, he consistently embodies a driven, physically oriented team member, with his development reinforcing his sports-centric values rather than undergoing significant personal transformation.