Mitsuki Hayase  

, 速瀬 水月

Mitsuki has both friendly relationships with Takayuki and Haruka, but harbors secret feelings for Takayuki. In high school, she was a skilled swimmer, but after Harukas accident, she stopped swimming to care for Takayuki. When Takayuki struggled with depression, Mitsuki tried to help him by expressing her emotions, which ultimately led to the revelation of her romantic feelings for him. Despite being well-intentioned, Mitsuki suppresses these emotions, causing them to accumulate and potentially explode in harmful ways. Additionally, she believes that she is responsible for Harukas accident because Takayuki was late for their date due to her actions.