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Mahiru Koizumi is one of the main characters of Danganronpa 2: Goodbye Despair. Beginning as one of the supporting character in Chapter 1, she became the victim as well as the main antagonist in Chapter 2. Even though she is dead in Chapter 2, she is also a posthumous minor antagonist in chapter three.
A strong-minded, commonsensed girl who is good at taking portrait photographs and has ill feelings towards men. She is the second murder victim, killed by a blow to the head with a baseball bat by Peko, who jumped in to do the deed to stop an enraged Fuyuhiko from doing so after he finds out she was involved in his sister's death, albeit indirectly. Her title is Ultimate Photographer.
Mahiru was also revealed to be one of the 15 Class 77-B members who were brainwashed into Ultimate Despair by the main antagonist in Hope Peak's Acadamy Saga, Junko Enoshima, in Danganronpa 3: Side - Despair. Mahiru made a cameo appearance in Side: Future when she was shown capturing photos for an also despaired Sonia Nevermind, who ruled as a tyrantess and lead a zealous followers with Monokuma masks.
In Side: Hope, Mahiru was awakened thanks to the hope power of Izuru Kamukura / Hajime Hinana, and then she helped Hajime in stopping Ryota Mitarai's plan of spreading his brainwashing hope video. Finally, after falsefully yet willingly taking blame of the Final Killing Game and was determined to atone her crimes, Mahiru eventually went back to Jabberwock Island with her classmates in order to start a new life.