Trash should be disposed of.
I agree, especially if it wasn't their first time. With that said, I question— based on how lax Eri was about the situation—if they've ever actually followed through before? Do they maybe just beat the women up (not great, but better than rape) to make them less attractive and hope they make the women regret it?
I mean, Eri hates the playboy for breaking her friend's heart, so wouldn't she have already murdered them one-by-one over time if they forced themselves upon women? She was willing to eat dinner with them. And the other female adventurers haven't joined together to kill them.
If nothing else, it's inconsistent writing.
There was no need to worry about their lives. His corny ass not-even-NTR backstory doesn't justify assault and rape of a completely innocent and unrelated person.
I'll just say that we have no way to know if it was more or less than than a one-sided fantasy. And if nothing else, I would argue that her response of "then prove it" shows she was aware and didn't bother cutting it off with the guy.
I suspect they're both bad people (if he's actually a rapist then he's obviously worse).
This also probably wasn't their first time.
Their behavior certainly makes it seem that way.
Here's my question: Where is the childhood friend now? Playboy is still around, and so is the dude, but she's talked about like it's a thing of the past. Did she run away to the next town? Is she in a brothel due to having no one to rely on after finding the playboy with another woman? Did she regret what happened, try to return to the guy, get refused, and then off herself? Was she the guy's first victim and her body is now under a garden? Or was she the guy's first victim and ran away because of it?
Way too many possibilities. I hope the story addresses it at some point... and I certainly hope she doesn't end up with the guy—unless he's trash, then they deserve each other (because even if he turned into trash, she was most likely given a fair warning about playboy and still abandoned the childhood friend who she knew liked her and would likely provide well for her in the near future).
By the way, we're discussing the behavior of fictional characters with people from around the world from a device in my pocket the size of a wallet... just slow down and think about that for a moment.