Okay, people. Prepare for another long AU. -cracks knuckles- This one has been boiling in my head so I needed to express it
An AU in which Jean is the direct spawn of Satan and Marco is the notorious One-Eyed Witch. The Devil is actually a woman, Jean’s mother, who seduced a righteous and innocent man, in hopes of defiling him to strengthen her offspring. Marco was born into a strong lineage of witches without two eyes, his only eye being his tool to “only see the simple truth”. A second eye would have created a bias or corrupted his perception of the actual truth.
The Devil was able to steal a significant power from Marco’s family, whose duty was to protect and guard this immense power given as a gift from one of the Gods. With this power, the Devil could completely taint and destroy anything she pleases, which she’d take full advantage of.
Because Jean’s father was so righteous, instead of just being born more powerful, he also was born without inheriting his mother’s rage and darkness. So, it actually becomes his fate to kill his mother and steal the power back. But he can’t give it to Marco’s family, seeing as he’d absorb it instantly and would be unable to control it.
While Jean is destined to kill his mother, Marco is destined to re-attain the power that was stolen. He’s actually supposed to kill Jean after Jean kills his mother to get it back. The two know of this ultimate end and before they’re able to comfortably accept it, they fall in love during their time together hunting Jean’s mother down. Marco scrambles to try to figure out an alternate way to gain the power back without killing Jean. He studies spells and exorcism techniques, unable to find a sure fire way. It nearly drives him insane, being faced with the fact he will actually have to stab the love of his life in the heart and kill him..
But in the end, it turns out there is an alternate way of regaining the power and sparing Jean’s life. Marco has to transfer Jean’s soul into another vessel, use that vessel as a sacrifice to get the power back, and ultimately return Jean’s soul back to his original body.