Asuka lives together with her parents and Kasumi, whom she simply refers to as "onee-chan" - however, it's not always clear who is more responsible out of the two. She is a year younger than Kasumi. She is much calmer than her sister and tends to be sarcastic, and is bad at showing her affection towards Kasumi. According to Kasumi, they used to fight all the time when they were in elementary school, but nowadays they get along well; Saaya even says that they're like good friends and she is a bit jealous about it.
In the 2nd season, Rokka had invited her to form a band with her but she declined. However, she promised to keep an eye for Rokka for possible band members.
In the 3rd season, Rokka finally met her "fated band members" and Asuka's role of watching over her ended. She then volunteered as a staff for the event "BanG Dream! Girls Band Challenge!", and watched Poppin'Party, Roselia, and RAISE A SUILEN perform together at the Budokan.
Toyama (戸山): To (戸) means "door, entrance" and Yama (山) means "mountain". Toyama also refers to the Shinjuku ward.
Asuka (明日香): Asu (明日) means "tomorrow", and Ka (香) means "fragrance, aroma".