Not much is really known about Irisu save that she was distant from other children during her middle school days. She particularly bonded with a neglected school rabbit, which helped to develop her obsession with rabbits like that seen of the fake rabbit ears sewn to her hat. This led to her breaking emotionally and mentally once the rabbit was killed. She withdrew but later encountered and fell in love with Uujima Satoshi. (Rather sickeningly, they particularly bond over Uuji's sadistic images of cats being tortured, although her hatred of cats stemmed from finding her rabbit's head being licked by a cat.)