The Ghost of You - Septiplier x Danti
Mark and Jack have been together for a few years when Dark returns, after being absent since before the pair met. He notices the chemistry between them and at first, finds it pety and mocks Mark, but then he realizes he could have someone like that of his own that he could cause havoc with, thus creating the demon that is Anti.
[Cover art made by @WooshieRinu]
[Somewhat AU - Contains violence, lemons, and cursing]