I've worked it out.

This is the last panel of the prophecy. It was in our fucking faces, all along.

Kris is possessed by Chara, or something similar. But it's not a demon, it's an angel. Someone like you, someone playing a video game, only they're a massive shit about it.

And what can you possibly do to an entity like that? Violence won't work, the fourth wall is infinitely thick.

You need to get them to go away.

You need to bore them until they give up and leave.

You need to banish the angel's heaven, the reason why it's here in the first place.

You need to get rid of the Dark Worlds. Forever. Without them, it'll eventually fuck off.