So basically lil' D is telling a half truth; Yoru wants to use the black chainsaw devil to *eat* her, which he cannot do if he gets turned into a weapon. Actually, that probably why she didn't turn him in the shop; not out of love, but it is the he is the only way she can permanently get rid of the Death devil without it just coming back. Yoru is definitely going to offer him sex again if he eats the death devil.