Her design appears to be influenced by the characters of Pure White Lover Bizarre Jelly. She is a little girl with large blue anime eyes and green hair. She wears a white school swimsuit with the numbers 4-2 written on it indicated her year and class in school, on top of which she wears a powered suit weapon. The armor on her arms and back seems to function similarly to Nathan Copeland's boombox; blue, yellow and red colored arms and weaponry devices extend from her Japanese primary school-style backpack to which she is also strapped by what appears to be danger tape. The large plate over her backpack is in the shape of the kanji for moe. She could possibly have an Indian accent. Her accent may be Irish, which would make sense since Henry was raised in Ireland.
Henry encounters Mimmy when he awakens on a hill of flowers and notices a little girl with giant robotic arms. She first approaches Henry kindly and seems to be able to read his thoughts and teleport them from one place to another, which might be places in Henry's memories. When Henry expresses his wish to leave, Mimmy tells him she won't let him, claiming that if he defeats her he can leave, although she first asks Henry to stay with her forever and says that their two consciousnesses are now one. Henry in turn requests that she joins him in returning back to reality and that she "might like it there." She then appears behind him and claims that he is lying, after which the fight ensues. When Henry defeats her, he drives his sword through her back, whereupon her robotic limbs and back plate shatter. She then inflates and explodes, after which the game claims that she has "disintegrated", and Henry wakes up.
She seems to be able to manipulate her power suit as she can change the size of her suit's hands when throwing punches to unnatural proportions and seems to be able to transport very quickly as well as fly. She also uses the suit on her back for an assortment of attacks, which include launching missiles, shooting twin laser beams from a beam gun, and flying above Henry and crashing down on him.
- In an earlier version of the script, rather than inflate and explode, Mimmy was supposed to turn into a nightmare with bloodshot eyes at the end of her battle. This would have made her even more similar to the Angel from killer7, who also has bloodshot eyes after being initially defeated; Mimmy and the Angel already share the similarity of being inexplicable "cute" anime designs in games with otherwise semi-realistic designs.