@Happily_Grim
Eh.. I mean.. I'm a WN reader as well. I'm pretty confident he raped her.
It's just that she became willing part-way through, and then his endless stamina made her realize she can't handle it all on her own.
The transition is him looking down at a naked girl in front of him who's backing away to saying something along the lines of, "what a great night."
But yeah, it's definitely ambiguous, and I personally hate rapist MCs myself, but can't really see the first time any differently. Maybe the author got shit for doing it that way, and went the opposite way in future chapters? I don't know. I never read the original Japanese and its comments.