In this adult sibling role-play, Saori had been living alone for her pin-up modeling career, but she quits the job and returns to her rural family home. When she sees her adult younger brother Taichi again, he has grown into a big man but is still a shy virgin who gets flustered over a token Valentine's chocolate. Saori exposes her cleavage to tease and seduce the inexperienced Taichi, only for him to become far hornier than she expected and push her down. From that day on, Taichi turns into an insatiable sex beast, relentlessly fucking his busty, defenseless older sister throughout the house with nowhere for her to escape.