Makoto, a university student living with his older brother and his brother's wife, is heartbroken after a painful breakup. Seeing his distress, his sister-in-law, Sayuri, attempts to comfort him by unexpectedly exposing her breasts, insisting, "Here, let this cheer you up... you can rub them as much as you want." Makoto finds himself unable to suppress his excitement in the face of Sayuri's beautiful, large breasts—which far outclass his ex-girlfriend's. This encounter takes place one night while his brother is away on a business trip; however, Sayuri's "erotic kindness" is actually driven by her own deep sexual frustration stemming from a sexless marriage.