Tanbecca

Tanbecca is the crackship between Tanner x Rebbecca.

Why It Would Never Work
First of all, Waspshipping and Smoothshipping exist, and Necro ships Smoothshipping. (Plus I'm pretty sure smoothshipping already has descendants, so..). Another element as to why this ship could never happen is because of Tanner's mental state, since he's a psychopath. But, if he wasn't a psychopath, the following would probably take place:

It'd probably be a D/s relationship (stands for dominant/submissive), with Rebbecca constantly feeling the need to take care of Tanner and Tanner calling the shots before Rebbecca. She'd feel this way because of the fact that "well he's a big scary demon he can protect me" and the likes. Over time she'd become more reserved and timid, and less like her usual self. Plus, if Rebbecca was about to be ran over by a car or something, Tanner probably wouldn't be able to save her and wouldn't even try if he could.

Second of all, Rebbecca has a boyfriend already. Which is why all her new ships will be crackships.