Did someone say genocide?
Time to talk about who and what demon you would spare and which you would annihilate!
To make it easier, imagine that you're like Yuyaa, a commander of an army and your job is take back the city Kazuya goes through from the demons. In that scenario, I'd seal the doors of the Shelters Kazuya woke up in since it's filled to the brim with demon dogs that might genuinely be too dumb to really reason with and plant demons whose litteral purpose in existence is to make lamps with the soul of the humans they manage to seduce. I'd assume that eventually that'd make them leave.
Like back to the demon world? I forgot that part of the lore honestly. Anyway, wipe out the harpies because they're birds of prey that focus on the weak and injured. I guess one could leave the Echos alone...unless one of your men dissapears. (I forgot how obvouis it to notice if one of them was brainwashed into being an Echo's lover or if they're just that horny)
No need to worry about the Sphinx, Haru and Liz, Mother Rabbit, Time stopping Doll, Cruel Spiderwoman and the Black Coffin monsters since this is post Kazuya's adventure and they would no longer be there in the first place.
I guess the Spider's nest and familiars still remain, if so...honestly, I'd say a coin toss on deciding to even try to enter that place to free any humans sealed inside there since it's unlikely they might still be alive or even capable of recovery (they literally turn into goop slowly irrc). And I think that's all? That really wasn't much of a talk now that I think about it.
Oh, forgot about the bird demons with parasite tails. I think they're a TPK (Total Party Kill), they're super fast, one stab of their tail and you're their slave and I don't see how you'd repel them without a specific strategy in mind.
So new question, what are the odds of survival in that world when you're not Kazuya? For one you wouldn't have Black Coffin demons send your way but you also don't have magic and will have to rely on the equipment you can find.
If you wake up in a shelter, or well, the shelter then you're just out of luck. One of the dogs or Lampas will get you. If you're in the city, then as long as you got a weapon and don't have superbly bad luck, then the harpies won't bother you until you show any sort of weakness. Just don't go to the Park with the Echos in it too, (I'd assume there'd be big graffiti letters warning about the place having brainwashing mermaids inside them at the entrances of it) but to make a long story short.
Unless you're lucky and find a really strong weapon with decent ammo, the moment you meet a demon of reasonable strength, it's just game over.
