I became the boyfriend of my senior at work, Saeko, but she didn't let me have sex because she didn't like my virginity. So I tried a dating app and met her older sister, Mariko! Her husband is on a business trip abroad, and she's quite frustrated. We started a secret affair... Unlike Saeko, Mariko lets me have sex with her, and it's so good that I feel like melting! Our desires escalate, and we even sneak around at home...