Satanic Rituals And Their Time Space Time Applications Adventure Time AU

Prologue

It's been about three days since the epic showdown with Golb. Except it wasn't all that epic, because if it weren't for Betty we'd all be dead. But it was Betty's sacrifice that caused her fiancé, Simon Petrikov the most pain. Without Betty, he was just a half of a pair. Without the crown, he was just normal. There's nothing special about a broken old man in a magical world. Nobody's even around to remember him anymore.
Nobody except—
"Simon?"
Simon stops writing in his new journal. (Which is probably a good thing, because it was getting way too meta tbh)

Marceline has come to visit Simon in the Ice Kingdom to see how he was doing. He said he'd be cleaning, so why is he in the corner being sad again?
"Simon, where have you been? We've been looking for you! Are you... doing okay?"
Marceline notices the dark circles in Simon's eyes. He hasn't been sleeping.

"Marcy! It's good to see you... I've just been here. Thinking." Simon looks up at Marceline. She's grown so much, he hasn't really had time to marvel at the girl who he once protected during what seemed like an abandoned world. But now there's life everywhere, intelligent beings that evolution would have never naturally created. Simon unconsciously continues to write in his journal "Maybe that's just how things are meant to be. To change.—"

"Simon, you need to get out of here. I think wallowing in your past is really messing you up. We're having a party tomorrow. You coming?" Simon has always been like a father to Marceline. Even more than her biological father, Hunson Abadeer, ever was.

Simon closes his book and stands up. A sheepish smile comes across his face. His dear Marceline. How has she been able to go through with this as long as he has? But she is right. He needed to get out of the "the past" room.

As he gets up to leave the room with Marceline, he knocks into a shelf and a book falls to the ground, face down. He reaches to pick it up, only to hear Marceline, who is already in the hallway, yell for him.
"Simon! Let's go!"
The book can wait. Let's just get out of here.