Yumi lives with her older brother and father. Her brother accidentally sees her cleavage and is shocked by her massive breasts, instantly getting an erection. "Those tits are totally unfair!" he thinks, and ends up masturbating thinking about his sister. A handsome private tutor who comes to their house twice a week also has his eyes on Yumi's huge breasts. Meanwhile, their father often has Yumi wash his back, and though he pretends not to notice, he secretly enjoys it. Realizing he's the only one holding back, the brother sneaks into Yumi's room while she's asleep and attacks her.