Taisei Uinchashi stands 183 cm tall with a muscular physique as a third-year Doshisha University student. He plays left flanker for the university rugby team, wearing jersey number 6. His appearance features short, spiky dark blonde hair accented by a small red-dyed front section and brown eyes. He has blood type A and a birthday on May 26.

He projects an authoritative demeanor, commanding strong respect from teammates who see him as the likely successor for team captaincy. His strong-willed nature fuels frequent disagreements with fellow player Ibuki Ueoka over team dynamics or strategies, underscoring his evident leadership qualities.

He was among the team members present and surprised by Natsusa Yuzuki's announcement of transitioning into a managerial role.

His name "Uchinashi" combines "inside, within" (内) with "pear" (梨), while "Taisei" translates to "big, great" (大) and "become" (成).