Seeing my friend having sex with my sister, and being unable to bear sleeping with her, as I, Nagase Asami, NACT-009

I was drinking at home with a long-lost relative and her sister, Mami. We talked about our recent lives and reminisced, and in our high spirits, we drank too much. I was allowed to stay overnight and went to sleep first. In the middle of the night, when I went to get a drink because I was thirsty, I witnessed a scene I 'shouldn't have seen'! Still excited, at the family gathering the next day, in front of my drunken and unconscious relative, I...