First one up is a DC comics one. Powergirl wants to be digested by Supergirl. Problem: PG is invulnerable and is therefore immune to digestion. Solution: PG visits Zatanna to have a spell cast on her that removes her invulnerability and allows her to be digested. Supergirl is reluctant, but caves in.
Second idea, same as the first, except it involves Powergirl being unbirthed by Supergirl. Again, Zatanna helps out by casting a spell on PG to help her regress to a mere zygote within Supergirl's womb and become SG's baby.
The next two ideas are set in the Mass Effect universe. In both, Femshep finds out she can swallow people whole and digest them and/or unbirth people and regress them to mere human fetuses within her womb. She, of course, freaks out and swears to never indulge these newfound urges.
Spoiler: show
Third idea has Aria T'Loak finding out, but instead of using this as prime blackmail, she coerces Femshep into eating and digesting her. Femshep, of course, is reluctant. To sweeten the deal, Aria throws in an offer Femshep can't really turn down: Full and total control over Omega upon the asari's digestion.
Fourth and last idea has Tali finding out that Femshep can unbirth people and wants to become Shepard's baby. Again, Shepard is reluctant but gives in.