Toyama Asuka

is Kasumi's younger sister. She is a first-year high school student at Haneoka Girls' High School. She is also classmates with Ako and Rokka.

Background
Asuka lives together with her parents and Kasumi, whom she simply refers to as "onee-chan" - however it's not always clear who is the more responsible out of the two. She is a year younger than Kasumi. She is a lot calmer than her sister and tends to be sarcastic, and bad at showing her affection towards Kasumi.

In the first season, she was a third-year student at the middle school branch of Hanasakigawa Girls' High School and in the same swimming club with Yuri.

In the second season, Rokka had invited her to form a band with her but she declined. However, she kept an eye for Rokka for possible band members.

In the third season, Rokka had met her and Asuka's role of watching over her ended. She then volunteered as a staff for the event "BanG Dream! Girls Band Challenge!"