MC incubus? / both of Ruby's meat sacks, possibly Abaddon's meat sack? Jo and then her mom. Asking Jo how she would feel if he made her mom happy, maybe saves them from the demon dog??? Lady Toni Bevell??? Bela Talbot. The darkness....Buys or takes the thief's soul from the demon and makes her his personal maid.
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Takes seal from Cain, slowly unsealing it so as not to hurt his future bride, decides to practice winning her with others first. Using possessed women as a good start, considering how similar their situations are, while throwing in some normal women, so he knows what normal should be.
.....FLASHBACK: What are you? Pick up in the future, in the empty where the explosion of Jack took place, waking up the true ruler of the realm, who meets with the empty guardian who bows before him, apologizing for his disturbed rest. The ruler then scolds him for his handling of Castiel before sighing and telling him to get back to work and let him handle it from here, but that there will be no next time for any future failures.
The ruler gathers all the memories of what's been going on and takes a liking to the timeline, and Amara, the darkness in particular.
Makes a human body??? Jumping into the timeline earlier, meeting and hooking up with Jo, eventually gets the mark, which he tries to adjust all the hate he feels into love, so Amara comes out better for him, his number one girl, who he intends to stay with for the rest of eternity after his mortal lovers die, shedding their mortal forms to live happily ever after. Twisting their dark forms together and falling into a deep sleep together. Knowing they would be together forever, asleep or awake.
The empty ruler is something before even god or death, the true first of the universe.
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Bela Talbot, first??? or maybe not, because she's too confident in herself. Maybe past fling, which she really loved, but ignored, and is happy to come back to him??? or not because she's a traitor???
...Was his first love, but she betrayed him, left him, broke his heart, and so now he's afraid to get with just one woman; he now fills the need to get many in case one of them breaks his heart again, he'll have the others to keep him together.
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....Hunters are more understanding of relationships, MC makes them more understanding.
Saves Jo, who went on a solo hunt after being frustrated with the way things have been going for her. Spends time together helping out and falling for each other.
Meets Jo and gets with her, teaches her, meets her mother, who disapproves, but one on one time he convinces her its the best option while seducing her saying things like if she ever wanted a son and saying he could be her son and that he was serious about Jo and he would be happy to make his mom happy as well as Jo watches secretly.
Telling the mom they both need him more than she realizes, they need to learn they need to be ready for the worst, this is life and death, not a game, and he will make sure Jo is ready so she won't die and her.
He moves up on her explaining how jo said she was alone and sad and how he could make that better, ignoring her poor protests as he comes around and slips a hand in her pants getting her off as she yells for him to leave to which he gives her a last kiss before finding jo who was excited by what she saw as he grins slipping his still wet fingers into her mouth while the other hand finishes her off while her eyes widened when she realizes what shes tasting, kisses her before she can say anything and then tells her to go take care of her mom. Chuckling as she stumbles away to her mother, who has yet to recover from everything that happened, and feels a bit uneasy and too embarrassed to notice her daughter's awkwardness when she arrives.
The two girls argue, but Jo tells her mom that he will stay and help teach them both and make them both happy, and that was final, which her mom accepts, wondering if Jo knew what she was saying.
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....OR AU Dean, more ruthless, does whatever it takes, enjoys the killing, more demonic.
At some point, he captures Ruby and puts her in a sex dungeon where he wets his dick with holy water before giving her all he's got.