Everybody here talking about whether it was rape or not, meanwhile I'm just wondering why he just automatically accepted her story, and why she immediately accepted that she was isekai'd and isn't freaking out and asking if there's a way to go home. Their reactions just seem too contrived, even for an isekai setup.
I mean I get that there have been otherworlders before, but it sounds like they're rare enough that he'd at least be suspicious of her. But then again, he didn't question his assumption about her being there to f*ck him or how she got in his (presumably) locked room, so he might not be the the brightest bulb in the box. Also, from the small glimpse we saw of her life before, It looks like she had a pretty decent life in our world, so any sane person in her situation would want to go home.
I love isekai trash, but this might be too much for even my suspension of disbelief. Well whatever, someone obviously liked it enough to take the time and effort to translate it, so maybe it gets better or the the things I mentioned are addressed later in story.