Mitsuki is friends with both Takayuki and Haruka, but secretly she has feelings for Takayuki. In high school she was a competitive swimmer, but shortly after Haruka's accident, she finds herself leaving swimming to tend to Takayuki. She throws herself at Takayuki when he fails to climb out of his depression, and reveals her feelings for him. Mitsuki is well-meaning, but suppresses her feelings, allowing them to bottle up and explode in dangerous ways. Mitsuki also believes that she is responsible for her friend's accident, as she was the main reason why Takayuki was late for his date with Haruka.

(Source: Wikipedia)