Udagawa Ako is a first-year student at Haneoka Girls' High School and Roselia's drummer. She admires Yukina and her older sister Tomoe, and is the best friend of Rinko, whom she calls "Rin-rin".

Ako has chuunibyou tendencies, and has illusions of grandeur and magical powers. Rinko suspects this is the result from her playing online games frequently. She enjoys playing the role while keeping a realistic mentality. She is very cheery and noisy, and, despite only being two years younger than the other band members, is treated like the kid sister by the other characters due to her childlike appearance and personality.

Ako often wonders how she can be a "cooler" person, and sometimes feels inadequate compared to her other band mates, especially since Yukina and Sayo occasionally ignore her or scoff at her ideas at times.