Deltarune Spoilers. Thinkin' bout the prophecy.
I keep coming back to the idea that the 3 heroes of the prophecy are Kris, Dess, and Asriel as opposed to Kris, Susie, and Ralsei.
Kris is the only human we know about, and the "cage" is a pretty accurate description of them, no reason to doubt there.
For Susie, we learned in chapter 4 that Gerson, a character pretty intimately familiar with the prophecy doesn't consider her role to be of one of the heroes (Specifically, he calls her the "Dragon)
For Ralsei and Asriel, as of chapter 5 we know a few things:
1) Ralsei has been since the beginning shoehorning himself into the prince role because he believes he's meant to be that part of the prophecy, but as the game continues it gets clearer that he doesn't fit as well as he's made it out to be. Even as far back as chapter 1, Ralsei is first shown with his cloak, made to match the image of the hero in the legend
...Which he promptly ditches about 10 seconds after meeting Kris and Susie.
In chapter 4 we actually get to see the prophecy as it's actually told vs the version Ralsei relays to us at the beginning.
When we look at "the girl" here, she doesn't quite resemble Susie, does she? Most notably, she carries a sword as opposed to Susie's ax. It seems Ralsei has just projected that role onto her due to her appearing before him.
But that's not the only Hero who's description has been a bit changed. Ralsei describes the prince as being "From the Dark", a description that fits him as a darkner. But looking at the actual prophecy, all it says is the prince is "Alone in deepest dark". This doesn't really imply the prince is a darkner in the same way that Ralsei's version does. In the same way that he's projected Susie onto the second hero, it almost appears he's just projecting himself onto the prince rather than knowing the prince is himself.
With chapter 5, his big focus for the entire chapter is Flowery trying to goad him into abandoning the idea that he needs to be "playing his part". Ralsei has been being encouraged by Kris and Susie to try being his own person a few times at this point, and has come a far distance from chapter 1 where his only sense of identity came from being the prince. To the extent where being forced into his old chapter 1 outfit by Flowery upset him. Additionally, chapter 5 sets up the idea that Ralsei likes the idea of getting to be a princess.
He has this idea in his head that if he lets himself do the things he wants, the world is going to end. But is this really the case?
2) The dark worlds and fountains have been being created as far back as when Dess disappeared, and chapter 5 confirms Ralsei didn't know anything about this. He's always had an inexplicable knowledge about the prophecy since he first showed up, and the idea that the events actually started unfolding presumably before he even existed leaves him visibly shaken. Considering the events that are supposed to kick off the prophecy is the creation of new fountains, shouldn't then the people who were around at the First round of dark fountains be the actual heroes of the legend?
Kris is pretty heavily implied to have been involved with Dess's disappearance somehow, and has a lot of preliminary knowledge of the dark worlds. Dess is heavily implied to have visited dark worlds of her own volition. Asriel was close enough with her to have left his belongings in her room, be voted festival King and Queen with her, was in love with her. Did he go into the Dark with her?
3) Asriel is the son of Toriel and Asgore. At this point we've seen both their appearances in the dark world.
Where they are shown wearing a Queen and King's crowns respectively.
Would this not make Asriel the Prince in the dark?
Then there's the fact that Ralsei looks extremely similar to Asriel as noted by some of the other characters.
Though chapter 5 includes an interesting line from Asgore himself on the matter:
Yes, the fact that Ralsei is a darkner and not a monster is certainly part of this, but I think when you combine this with my earlier point of Ralsei projecting himself onto the prince's role you get something like:
Ralsei looks a bit like the role Asriel would've played here, but the more you look into him, the more he seems to be something else entirely.
... so that's it. I think Kris, Dess, and Asriel are the heroes who started everything. Though I am unsure how they're going to come back together to end it all.
