"Two days of fumbling with my boyfriend's sister"

Rio and I have been in love for a while. I love her very much and promise to marry her. But when Rio had to go on a business trip for three days, Miru - Rio's younger sister, dropped her keys and had to stay at my house temporarily. During that time, I was seduced by Miru.

Although feeling extremely guilty towards Rio, Miru's beauty and cuteness made me unable to resist. I quickly ran out of sperm by Miru, I gradually developed feelings for her, thinking that these three days would be the most difficult days of my life, but no, these are the best three days of my life...