Asuka is Kasumi's younger sister. Currently, she attends Haneoka Girls' High School and is classmates with Ako and Rokka. She previously attended Hanasakigawa Girls' Junior High School, where she was in the same swimming club as Yuri. Asuka is a year younger than Kasumi, although Asuka appears to be the more responsible one of the two. She is calm, level-headed, and tends to be sarcastic and bad at showing her affection towards her sister.