Koichi, whose mother had huge breasts, was only interested in women with big breasts from a long time ago. One day, Yoshiyuki goes on a business trip and accidentally looks into Yui's masturbation, which has a lonely body. Koichi couldn't help but be amazed by the sensitivity of Yui's beautiful breasts, not that Yui was masturbating. The next day, Yoshiyuki returns from a business trip and sees that the couple has fallen asleep, and Koichi crawls into Yui's futon...
