Dear people reading this story: I am an awful person. While others would imagine the scenario of Rin defeating Satan and becoming the ruler of Gehenna in his place would be a good thing, I have to be the black sheep and make a sad version of that. And this isn't a "Rin becomes a villain" story, either. Long story short: this story takes place in a world where Rin sacrifices his body, becomes one with Satan and is condemned to residing in Gehenna…and this is not a happy thing. I repeat: I'm an awful person.
With that said, enjoy this fic if you can.
Disclaimer: Blu Rose doesn't own the Blue Exorcist series, only this fic.
Summary: As he is now, only being able to observe his loved ones as phantoms occasionally while the literal Devil is constantly tempting him, Rin can only think that this must be hell.
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He wasn't quite sure how long he'd been here in this particular spot. It may have been minutes or hours, days or months. Time in Gehenna was weird like that. Rin doesn't know anymore, and he sometimes thinks that he doesn't care. After all, he no longer has a body to be held down by things like hunger and fatigue—just blue flames that he's forced to share with the consciousness of the former God of Gehenna, who occasionally tries to make him carry on his work.
But he doesn't care about that bastard or the few minor demons who have the balls to approach him like he's the second coming of Satan. There are only two things that Rin finds himself thinking about anymore: destroying hostile demons before they can make their way into Assiah and observing the phantoms of those he cared for.
If there was one pro to no longer having a body, it meant Rin was no longer unable to see his friends due to distance or finances. Of course, the distance between Gehenna and Assiah was different from Tokyo being miles away from Kyoto or Inari. And he couldn't really see them whenever he wanted. Humans were only ever visible in Gehenna when they were prime to being possessed by demons, appearing like ghostly apparitions. Rin wasn't entirely sure of the mechanics behind it, but it helps him to protect people from ground zero and it lets him get the occasional glimpse of his friends—if only during the moments when they were in pain. And those moments were far and few between, just the way Rin liked it. A glimpse at his friends wasn't worth their pain.
Rin would rather enjoy the rare glimpses at his family. Even though he can practically sense that those glimpses are only possible because he caused them pain. He sees Yukio often—his younger brother feels guilt for not being able to save him or stop him. He sees Shiemi when she either feels as if she wasn't strong enough to save her friend and brother-in-law or just plain misses his company. He sees his wife as she cries herself to sleep at night alone, not wanting to move on no matter how painful it is to remember her husband. His son, who was in that "rebellious teenager" stage, had even more of a reason to hate him: for making everyone sad and leaving them—for leaving him behind when he still needed his father. Everyone seems to think that he died taking down Satan, and while a part of him wants them to show that he hadn't died like some tragic hero—that he still existed, if only on another plane of existence, he knows that isn't possible. Not without possessing someone or risking someone's life, and his conscience wouldn't allow him to do such a thing.
Satan whispers often to him. He claims to know Rin's pain and desire, and tells him to just reach out and take what wants. If he wants a body that's strong enough to not die or burn away, why not Yukio's? He's so strong now that he's awakened his demonic side, no longer a runt is he! And it's a waste if he doesn't use that power as often as his elder brother and "papa". Or better yet, why not his son? His body's already like his father's in so many ways, perhaps all he needed was a push to see if he inherited more than just blood from dear "grandpa". Either one's good for the taking with the turmoil their hearts are always in—he could just take one and step back into Assiah…smell the air…feel the sensation of flesh and bone…embrace his friends and family…
When his so-called father tries to tempt him into doing such a thing, he thinks about his loved ones: his dear friends, whom he's sure are leading happy lives. His successful little brother and his wonderful sister-in-law. His beloved son, whom he wanted to grow up like a normal kid. His dear wife, whom he'd protect even from Gehenna. Kuro, whom he often apologizes to for leaving behind, though he knows that his family is taking good care of him. Rin thinks about how badly he wants to see them all again, almost enough to risk having them be engulfed in blue flames, or be exorcised like the inhuman thing he was now.
…Never. Not while he's forced to share a consciousness with Satan. Not while he's like this. If he had to choose between potentially harming those he cared about and being forced to watch them when they're in pain and suffering, he would choose the latter. But while he tries to make himself content at the sight of his son cursing his name for the umpteenth time, Rin momentarily thinks that this is hell.