Momona's fiance is a loser, he drinks, gambles, does drugs, and abandons his fiancée to avoid debt. From then on, Momona did not leave the house, her face always showed sadness. Today, Momona's younger sister Sayuri brought her boyfriend to her house for the first time. Tsubasa was attracted to Momona's big breasts from the first time they met. Maybe because she hadn't had contact with a man for a long time, Momona knew that Tsubasa was looking at her breasts but didn't hide them and deliberately let him see them. Seeing Tsubasa's cock in Tsubasa's pants made Momona's long-buried arousal awaken. And when the two met in the bathroom, Momona couldn't hold back anymore and actively sucked Tsubasa's cock. And just like that, their secret relationship began. The two continued to fuck each other whenever possible even though Sayuri was still right next to them...