While I will eventually write it down, reader's point of no return is when it seems that they will be rescued by another group of hunters while siren!Doppio and harpy!Diavolo are out, as reader is mostly harpy at this point- but when the hunters do see them, all the hunters see reader as a feathered monstrosity and point their guns at reader.
That's when reader fucking snaps- the crushing realization of they're irreversally changed and no longer seen as human makes them go feral, and they kill most, if not the entire group of hunters and start tearing into the bodies to fill their stomach.
Needless to say, siren!Doppio and harpy!Diavolo come back to several bodies torn open and (now) harpy!reader swallowing chunks of human meat whole and now have to calm them down. (harpy!reader eventually recogizes their boyfriends and ends up huddling and crying between both of them because at this point they see 'safe' after all the stress and sex with them both has fucked their brain over on top of the new harpy instincts bouncing in their brain)