the authors include it because they find it hot….I’ve read author interviews to try to understand why this stuff is so common and it’s literally because Japanese fans enjoy it….
While I am very disappointed by how the SA was handled (especially for the "friend", it's unfortunately easier to see that happen for the stepdad just because it would be a lot of energy to inform to mom, potentially take care of her afterwards, deal with the police, etc. But the "friend" did not need to reappear at all and cutting him off would have been totally easy) , I don't think it was used for that purpose of fanservice in this case, since the act is not shown.
That being said, the author really needs to show more that they understand what victim blaming is wrong and complete bullshit, and that maybe sa-ing a guy and trying to post his nudes on the internet because he treated you like an idiot just shouldn't be a plot point at all
Y’all I know it’s compact and a lot to cover in 6 chapters but like… Why was his SA just glossed over… Tou my poor baby he needs the happiest of lives after all he went through