The seme loses his memories after a traffic accident (I want to say motorcycle). He was straight before and so the uke keeps it a secret. Believe they went to school together and the uke was in love the whole time. The seme also finds the uke's sister attractive and "falls for her" when he doesn't have his memories. Think the uke masturbates to a sex tape of the two, but not so sure about this. Sorry about the limited info

It's Mou ichido, nando demo. 🙂 .