Really? I personally think the hentai is necessary. Not for fap material ofc but already traumatizing as it is, the hentai part of it shows more detail of how the characters feel and what its like going through it. Since this hentai is based on true stories, there’s nothing to hide if you’re going to tell the cruel reality and truth of it anyways.
I will explain. For me there is a difference between hentai (porn) and NSFW material that is needed for story telling. The fact that we are presented with a young girl being raped by her father and growing to enjoy it is horrifying and is nothing but fap material.
There are plenty of manga that address what's happening without turning the victim into a pornstar and that's exactly what this manga did.
Honestly, awareness that shit like this actually happens is important. We can't keep failing victims, male or female. However, presented as a hentai was probably not the best path.