C lassmate of Hotaru, Chieri, other canon characters, and eventually Kirai. She loves being a superhero and helper like on her favorite magical girl and superhero shows. She hosts Kumako after making her mom come to Nodoka's home to give her explicit permission when Chieri showed Mogu her sister's Parasite Void.

Before moving to Kanzakai, she was born and raised in the Miyagi Prefecture. Unfortunately, she was in the heart of the devastating Tohoku Earthquake and was forced to relocate with her mother, who had divorced her father around the events of the aftermath. A lot of her behavior stems from the disaster's impact on her life, always wanting to be a hero that's a step ahead of any tragedy. Enrolled in Iroha (tentative) Academy and determined to become a hero to all citizens (due to her tendency to bingewatch shounen anime,) she started the Hero Club, endorsed begrudingly by Kougami. She started her streak of good deeds not purely out of an inherent want for justice, but because she always wants to prove that she can be there for others right away. Hotaru, Chieri, and Kirai eventually all join. They focus on helping people around the school building during extended hours, but when there is nothing to do all the kids just cause a ruckus and play games. While she never brings it up, it seems she was rather lonely before Chieri became friends with her, and never had many lasting friends due to moving. Her mother also seems to be kind of neglectful.

Despite being a host for Kumako, she seems to not understand anything about the Hollow Night beyond the surface level information told by everyone else. Mogu tends to be very nosy about it and tries to force herself into it in order to help, typical of her nature. Due to her young age, she is naturally denied to help by Nodoka, Aoki and Tsujino very often, but she still attempts to regardless, sometimes stumbling into the Hollow Night herself with only a practice weapon. Ruru and Bernie, however, are predictably indifferent.