She is an immortal as well, and appears to have a bright personality. She is fond of alcoholic drinks despite looking like a teenager.
Her job scope includes financial management, information processing, and other miscellaneous tasks.
She cares for Rin very much and would do anything to ensure her safety, even while nagging her to do the job properly.
She is a formidable hacker. SpoilerWas outmatched by Katsuyuki Kamiyama in episode four. After Rin disappears, she leaves with Genta and becomes a Buddhist nun. She feels indebted to Rin as Rin saved her from being devoured by an angel during their first encounter and has been protecting her ever since. In episode six, believing there still being a chance that Rin is still alive, Mimi constantly displays her resolve in rescuing Rin from Eipos' sadistic scheme.