真琴

The protagonist's younger sister, a first-year high school student attending a local school. She's on the swim team.

She constantly teases her brother with sarcastic remarks and often gets the better of him.
Being the impulsive type, she occasionally takes bold actions.

Her knowledge about sex is below average, and she's recently been troubled by a certain part of her body. Even so, she possesses deliciously large breasts.