Haruka's younger sister, She initially sees both Takayuki and Mitsuki as older siblings until she finds out they have been seeing each other behind Haruka's back. While Haruka is in the hospital, she visits every day since there is no one else that can keep her company, even if Haruka is in a coma. This shows just how much she loves her older sister. She, like Mitsuki, is a powerful swimmer in her own right, but feels as if she can never match Mitsuki.
Source from Wikipeida