idk if your interested in this idea but how about a insanity mechanic where the girls spawn in normal but slowly erode over time both of them looking human at the start but as they grab you you loss 10% saneity and after you hit 50% their skin turns white
at 70% they start to bleed
80% they start to mutate aka the girl who becomes legs turns into legs but the main girl maybe starts to have her pussy turn into a monster of tenticles where she wraps them around your balls and pulls you into her
at 100% you loss your mind fully and a end screen is played with you glitching in and out of reality where we see our boy raping the two girls while their collared and have injures from him trying to defend himself hence the blood he sees
yes this seems fucked up but it made me think about the discoloration and other games that slowly make the mc go insane
my thoughts is the story could be about him loving these two girls and as they get captured our man maybe suffers some mental issue that makes him go insane and attack them and after he snaps he thinks their fucking him but the truth is he lost his mind and is raping them
a end statement could have a text screen or a voice action talking as the girls mentioning they heard him screaming to get away from him and stop fucking him while he was breeding them