Karen is a shy and well-behaved girl who appears serious both at school and at home. Since moving to a new town, she's made few friends and feels increasingly lonely. Ever since childhood, she's harbored deep feelings for her older brother, emotions she's never been able to share with anyone. Unable to confess her love, she's resorted to daily masturbation to cope. Eventually, her pent-up desire becomes unbearable, and one day her lust spirals out of control. Torn between her forbidden emotions for her brother and her uncontrollable urges, Karen takes her first step into a new, secret world.