After Erina gets sent back to Rabi Rabi Island for the first time, she ends up falling asleep on Irisu's lap.

Irisu has been friends with Rumi and Erina since they were children. She's a very timid person who enjoyed playing with Erina when she was a rabbit.

She is always secretly stalking Erina, but unable to talk to her face-to-face. She ends up running away from her any time they meet.

Her love for bunnies was too strong. Going to Rumi's home to play with Erina wasn't enough. She had to have her own rabbit. She started recruiting people to look for bunnies and thus, the Usagi Pero Pero Club (UPRPRC) was created. It quickly got out of hand as their members kept increasing. The group earned a bad reputation because Irisu couldn't control their actions anymore.

Everyone thinks the rabbit ears she has are fake, and so do the members of the UPRPRC. Although, they're not fake but Irisu is hiding her true identity.

'Irisu' is a derivative of 'Alice', from Alice in Wonderland. The watch she carries, her rabbit ears and her tendency to run away are said to be related to the White Rabbit from Lewis Carroll's book. The game hints toward it with the final chapter's name: "Irisu in Wonderland".