Libra would stick his hand into your body like this over your womb and pull out your reproductive system, or a copy of it, wholesale. Not like gory though like its been removed, more like it's just displaced and he can access it externally now, it still effects you like you'd expect if they were the same organs as yours, and can still feel it like it was yours, because they are. So he slides it onto a porous pipe that he pumps alchemical semen and reagents into it to impregnate you with his homonculous "son", since that was the deal that was struck
Also maybe the pipe thing with it at the end, he uses it as a staff sometimes too so it ends up being that you can feel it moving around like a sex toy