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, Rio's younger sister, Miru, lost her keys so she had to come to my house to stay temporarily. During that time, I was actively seduced by Miru. Even though I felt extremely sorry for Rio, Miru's beauty and cuteness made me unable to control myself. I was quickly drained of all my sperm by Miru. I gradually had feelings for her. I thought these three days would be the most difficult three days of my life, but no, these were the three most wonderful days of my life.