So if any of these guys have sex, they somehow "destroy the world"? So... Why are they then tying these guys into chairs and almost literally taking their virginity by force and trying to get them to have sex? That makes... absolutely no sense whatsoever. We see that they're willing to shoot and kill any of these guys in cold blood, so... why not just kill them if they were that much of a threat? Why try and bring about the end of the world ON PURPOSE? I mean... even for an actual legit hentai/eromanga this plot would be dumb as dogshit.
Simple reason: For pregnancy. Remember, the girls are trying to save the world, not destroy it.
There are some lines about the children (of those virgins) supposedly will be born with immutability to the REAJUU (turn to a monster) virus, but might be I read that wrong (too lazy to check after so many blueball scenes).
There's no NTR. I know this because I actually LOOKED FOR IT and combed through the raws hoping it would satisfy my ntr needs. Lo and behold i wasn't satisfied at all. Disappointing.
Otherwise, please point me to the chapter number