Takashi, a virgin, heard from a friend that women also have sexual desires and masturbate, and out of curiosity, he makes his sister, Misato, give him a large amount of aphrodisiac. At first, he succeeds in watching the horny Misato masturbate as planned, but the drug works too well and Misato loses control of herself, finding him and grabbing his penis, taking his virginity. After that, he has nowhere to run until the drug wears off, and Misato, who has become an insatiable slut, attacks him again and again, squeezing every last bit of sperm out of him...