Succubus that keeps the portals open. Everything's fine on this end, that's not the problem. He's got his own tower overlooking a rift glowing with eldritch light. Strong flows of magic, lovely local ecosystem of gas-bladder borne creatures that warble and trill, of many-eyed thorny things that rustle and shriek and gnash.
But his best friend's on the other side. One of the last stubborn holdouts. That reality was built to die. That's what he's heard. That's what it's doing. But she was happy there, for a while. Managed to claw her way to some happiness, even run her own brothel, provide a slice of sanctuary in a bitterly mundane world. She's not leaving until the laws of physics rot. As for the things that come out of the deep to feast when a universe dies... "I'll handle it." That's what she says.
He's given up trying to talk her out of it.
Won't be long now. So, he keeps the portals open for his wayward sister. Hauling flesh-cables channeling raw magic, reengraving runes damaged by acid rain, keeping the sheets changed in the rooms on this side. Sometimes, when there's nothing that needs doing, he stands on a portal-threshold to watch the slow toppling of cityscapes that used to shine. Tombstones to a world undone, tumbling piece by piece into the void.
Watching for a familiar set of horns bobbing past the debris, for a sheepish smile, for a voice that says, "Hey, dorkcubus. Kept you waiting, huh?"