Sari's younger brother, Ken, is a diligent student at a boarding school who returned home for summer vacation. Sari, who had been lonely, was delighted by his return. To tease her inexperienced brother, she playfully showed him her bare breasts from behind and let him feel them, saying, "My tits are totally out right now~" However, this triggered an explosion of wild, monkey-like sexual desire that had been dormant in him! That single prank awakened his insatiable instincts. Now, using knowledge gained from porn videos, he chases her around 24/7, demanding to fuck her everywhere in the house...