> Incest: The dramatis personae (https://nhentai.net/g/609087/4/, mostly SFW if your boss doesn't mind fully-clothed underboobs) introduces the characters as step-siblings. (And page 11 the male character refers to the female character as "family".

It's not "incest" if they are not blood-related.

> Rape: The premise is inherently rapey as one is not allowed to withdraw consent after entering the room.

As I understand it, entering the room does not constitute giving consent, and one can withdraw their consent any time, which the protagonist chose not to do.

> Also the bottom of page 15 the male does not look like he had consented to the events of that page and the previous.

The way I read it, especially with previous two pages in mind, it appears to me that he does not mind.