Ayase is one of Satoru's classmates.
She's cheerful, responsible, and is loved and admired by everyone. After she was interviewed as the result of a certain newsworthy incident, she became somewhat of an internet sensation as a result of her looks.
Her bust size is E--that's what her bio says, at least, but that's a size she can only reach through extensive padding. Her breasts are truthfully a very modest size, so E-cups are nothing more than a pipe dream for her.
Her personality, like her breasts, is also fabricated. The real Mitsukasa Ayase is a bit lazy, moody, and prefers shutting herself in her room over hanging out with others.
(Source: Riddle Joker Wiki)
Content compiled by AnimeList.moe from publicly available sources.
