Mimi's past is mostly not known aside from how she has a younger brother who worries about her, she is an honor student of her school, and she is fellow classmates and friends with Illya, Suzuka, Nanaki, Tatsuko, and later Miyu and Chloe.
Mimi is a sweet and kind person who is considerate of those around her. Perhaps a little too kind and considerate for her own good, as demonstrated when Kuro drains her mana.
Because of a misunderstanding she saw between Illya, Chloe, and Miyu, and when Suzuka and her older sister introduce her to the world of doujinshi, she becomes a hardcore fujoshi. This side of her has made her very delusional if not out of control that her friends considered a lost cause.
Mimi is an average elementary school student with no special abilities.
She later gains a talent in writing BL doujinshi scripts after misunderstanding a situation between Illya, Chloe, and Miyu.
She is comedically shown to have a weak presence that can make her be forgotten or even ignored.