The main character is a virgin stay-at-home "otaku". His job is home security.
By chance, his father remarried and made a new family.
..Sister-in-law. Of course, her eyes were cold when she looked at me...and violent.
However, I both gasped and struggled with my sister-in-law in my new family.
My sister-in-law's sharp tongue was like a pressure point for me.
Then one day, I could not stand it any longer, and I determined to go out night crawling on day X in month X in year 20XX.
If I got caught I would be looked at even more coldly and may get punched and kicked.
I had to have sex with her without waking her up.