I Fell in Love With My Cool FWB but She Brought Her Big Breasted Sister Over

Kosuke and Sana met at university as friends with benefits, both uninterested in romance and focused only on satisfying their sexual desires. When Sana begins displaying increasingly endearing reactions during their encounters, Kosuke finds himself developing genuine feelings for her. After deciding to move in together to split rent, a third roommate arrives: Sana's voluptuous older sister Aira, a hostess who repeatedly insists on joining their intimate moments. As Kosuke struggles to understand Aira's persistent interference and its effect on his connection with Sana, he begins to wonder whether her sister harbors deeper feelings for him. What unfolds is a romantic comedy centered on desire, jealousy, and the possibility of mutual happiness among all three.