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Mahiru Koizumi is a minor antagonist in Chapter 2 and even thought she is dead in chapter 2 she is a minor also a minor antagonist in chapter three of Danganronpa 2: Goodbye Despair
Before the game she was being bullyed by Fuyuhiko Kuzuryu's yunger Sister insted of trying to work things out she help her friend Sato to murder her later she got rid of all of the get rid of all the evidence witch got her friend Sato was killed as an act of revenge but Mahiru Koizumi got a way
Later in Chapter 2 when she found out that Fuyuhiko Kuzuryu was the borther of the girl she help killed it shows that she feel a bit sorry for what she has done but then it turns out that she was in fact going pinned the blame on Fuyuhiko Kuzuryu witch then got her to get killed by Peko Pekoyama witch got Peko to be killed
In chapter three she is partly the reason with Hiyoko being the main reason why Fuyuhiko hurt him self to the point that he lost a eye and she was bleeding a lot and she is also partly the reason both Hiyoko Sanionji and Ibuki mioda got killed and she is also partly the reason a long side Junko and Hiyoko to turn Mikan Tsumiki to become a murding pycopath after that she is a Comatose along side the other dead characters un a where that they are still alive in Chapter 1 she is a minor protagonist and is a friend of the main character.