I actually find the heroine kind of pitiful. While she was screwing over our MC, she was still following the route where they became friends and MC's life wasn't totally ruined - I actually initially guessed this was her attempt at actually wooing the villainess and not actually gaining the male harem (since it was the only good ending for MC), and in a way I was kind of close (it was just self-love instead).
Now she's really and truly alone, enslaved by the obsessive original persona within her mind. Neither sides of her really 'won'. The original heroine had her body stolen, defiled, and her reputation ruined by isekai girl; however isekai girl had no idea she was doing such. So I actually feel bad for the heroine in this case, I wish she was just a bit more hate-able so I could feel this ending was just.
I've seen Lucia's type of isekai before but most of the time its kind of treated as a joke or a minor plot point and never as a full on Horror film like thing.
I've said it in several of these isekais - I always found the possession aspect horrifying, and it really should be played with more. We've become so used to MC's just accepting it, so we now just accept it too, but what on earth are the originals going through? To them the isekai possessors must seem like horrid parasites who have taken absolutely everything - no one can even mourn what is essentially their death, because to everyone else they're still living!
The closest that comes to this is... well this comic, and "The One Within the Villainess", and I feel neither quite capture the grotesque horror of it.
I think another good idea would be the actual heroine being posessed, and waking up from the possession after the isekai girl has failed and left her in an awkward position; maybe a story about a family member realising what has happened to the possessed and trying to fix it.
Anyway, this was a good comic. Short, snappy, to the point (something we desperately need more of in manga), with a good concise plot and ending (also something we need more of). The art wasn't spectacular, but it more than did the job. This get a 'good outta ten' from me.
Thanks for the translations.