itch.io

For my fellow lurkers, the answer to this question is (as per the description once you've achieved it):
Get impregnated by one of your own children without a broken mind. I'd recommend doing this via getting impregnated by one of the maggots during the first wave. That way you don't also have to wait for eggs to hatch, as the flies are ready to go right after birth (though you need to get charged by them).