Mutsumi Wakaba is the soft-spoken rhythm guitarist of BanG Dream! band Ave Mujica, using the stage name Mortis. A first-year at Tsukinomori Girls' Academy, she is a former member of Crychic and childhood friend of Sakiko Togawa, the only one aware of Sakiko's personal situation post-breakup. Daughter of renowned celebrities, she feels overshadowed by her parents and blames herself for Crychic's dissolution. She experiences dissociative identity disorder, with her Mortis persona hosting hallucinatory plays reflecting her inner turmoil. Despite external pressures, she remains loyal to Sakiko and the band.