You don't need to write and develop a real romantic rival when you can just 2 page in some random cosplay slut and get the same desired effect, the youtube shorts of romcom writing
I can't get a read on Hinata. Her internal monologue is much more sensible the other girls and she doesn't seem to be overcome with lustful thoughts. Maybe she was also isekai body transferred from the normal 1:1 world like sou and is just trying her best to fit in to the new world.
I know that it's a story and the suspension of disbelief demands that the plot continues. But there's nothing really tying him to the mother and daughter, he could simply say 'no' and walk away if things get too weird.
Like he could have tried telling her to leave them alone. He pretty much invited her to continue trying to ruin his group. But yeah as people have theory crafted she’s probably into him and the reason for her death and subsequent isekaing is unknown.
It’s hard to put it into words. But it’s insult to injury that the girl that his best friend partially killed himself over Isn’t herself. Like it would have been more respectful to him if she stayed dead rather than whatever this is masquerading around in her skin suit.