Or maybe just directions I'd take the story if I suddenly had to write chapter 6 and 7 myself. Spoilers for Deltarune ch 1-5 obviously. This is partly just to show that there's not so much going on in Deltarune that the story can't finish in two chapters. I followed these guidelines:

• Can this be explained to players who aren't doing extra content?
• Can this be explained using YA appropriate language?
• Is it an interesting enough idea to make a game about?

The categories are the things I'm most sure of to least.

Most Sure

• In Deltarune, the body and soul are separate things.
  • The body reacts to stimuli and holds memories.
  • The soul is "the culmination of a being" and ultimately drives decisions.
• Something that will become important in chapter 6 and 7 are bodies without a soul and souls without bodies.
  • Beings without souls in UT/DT (that we know about) are basically just Kris when the player soul isn't in them and Flowey.
• Kris is just their body with no soul, and somehow a different soul was placed inside them.
  • This soul became controlled by the player at some point, but has been inside Kris while not being controlled by the player.
• Kris's original soul is missing. Dess's soul and body are missing, but don't have the be in the same place.
• The Roaring Knight is a fusion of Kris's original soul with Dess's soul.
  • In Undertale, a fusion of the human and monster souls could cross the barrier from the underground to the surface. The Roaring Knight appears to be the source of the Shadow Crystals, which seems to act as a way to see the light world from the dark world. The ultimate power of Shadow Crystals is being able to pass between worlds without changing.
  • There's some ways that The Roaring Knight looks like the amalgamates from the lab in Undertale.
• Kris's body is accounted for, but Dess's body is what's saying the unused script lines in each chapter's files.
• Dialog options are the memories in Kris's body giving the soul options on what to say.
  • Side B is something Kris's body wants to do (to find Dess's body?) but requires a soul to bypass resistance to what's required to make that happen. OR, something changed Kris's body to let Side B happen.
• Chapter 5 Side B's lake scene is creating a fusion of the player soul and Noelle's soul. During this process, Kris and Noelle's bodies become used up or lost.
  • There might be a change in the unused script in the chapter 6 files.
  • Some kind of barrier is being crossed.
• We keep seeing things about Kris's hand being lost.
• The moment where Dess and Kris's souls separated from their bodies and fused is a Side B style event, during which Kris's body was somehow saved from being lost in the game files and given the replacement soul.
  • Except, possibly, one of their hands. The hand we see in the game itself might be some other kind of thing.
  • This may have happened in the Dreemurr living room and involve Tenna in some way (there's lines about Noelle being surprised Kris gets rid of their tv)
• In Undertale, the barrier between the underground and the surface can be broken by a monster soul and seven human souls.
  • The mechanics of how magic works in Deltarune are slightly askew of how it works in Undertale.
• A lightener's appearance changes when they enter a dark world.
• The Roaring Knight has kidnapped lightener monsters who are in a dark world.
  • This is why, after trying for Toriel in ch3, the knight grabs Undyne as she's just as good of a choice.
  • A barrier will be broken by a fusion of the souls of seven lightener monsters changed by a dark world and a human soul.
  • This barrier will represent the difference between the game world and the "real" world.

Less Sure

• A Gaster like character is the game master of Deltarune, who decides the rules for other characters.
  • The goofy fucker Rouxls Kaard has Gaster face because he has a similar role, as a card who decides rules for other cards.
  • I'm going to call this entity Gaster but I think it's most likely to be a charicter that parallels whatever is going on with Gaster in UT.
• Giving rules to a game transforms what something represents. Example: when a carving of a horse has the rules of chess applied to it, it becomes a knight.
  • This is like how the darkness of a dark world gives life to darkeners.
• Deltarune is software being played on a fictional device.
  • Some characters in Deltarune seem to know they're in a game.
• Gaster is creating "My Deltarune" for a purpose.
  • Gaster has set in motion a series of events in the timeline of the story particularly to give the "game" this shape. This includes Dess's disappearance.
• A real danger to Deltarune characters is that if the player is given access to powerful magic, the player will misuse it.
  • Ralsei is limiting his power so the player doesn't use it.
  • The one time he allows himself to help the player without requiring commands, he ends up using fire magic on accident.
  • If Ralsei didn't use limits, we'd end up with a snowgrave type of incident but with fire.
• Deltarune is something like a show being put on for the player. Different characters have different goals, but are aware that they're in a videogame and that the player is watching and doing things in their world.
• The prophecy is the game's script, something that Kris as as the protagonist is locked into. This is like how in an rpg you'll get the same main quest line no matter what choices you make.
• The ending of Deltarune will be the characters talking directly to you, trusting you with power that you can misuse.
  • Toby Fox has said that he had a fever dream in 2011 about the ending of a videogame, and that will be the ending of Deltarune.
  • An ending where the characters of the game fight over a barrier between the real and game worlds.... that sounds like something you'd have in a fever dream.

Maybe (this is kinda just assorted thoughts)

• It's ambiguous if the dark worlds exist because of the dark fountains, or if they always exist and the dark fountains bring you there.
  • The characters seem to have a history that stretches before you get there. Is that history invented by the fountain or determined by something else?
  • This might never be answered, and the game might be better off if it isn't.
• The titans are born within a dark world when another dark world is made inside there.
  • Titans are called a representation of fear.
• Dark worlds are not presented as bad things.
  • Susie's life is improved by adventuring in dark worlds.
  • Darkeners talk about how they want to be useful to lighteners.
• I don't think Deltarune titans will be a direct metaphor, but whatever is going on will be applicable to choosing to use the things your brain makes up to build your character, or to create delusions within delusions and collapse in fear.
• The way light world sections of Deltarune are written is different than dark worlds.
  • The light world seems to be a more "realistic" world where people come off as simple and stupid, and when they contain emotional depths it sometimes just serves to make things feel worse. Things don't resolve in the storybook way like a dark world.
  • Dark worlds feel like an escape from these things.
  • The closest thing we've seen to this before is the dating scenes in Undertale.
  • This difference is already thematically relevant, but may become plot relevant.
  • This may also explain the decision to limit the amount of merch made for Deltarune lighteners.
• There's a lot of references to glitching through a game.
  • Ch. 7 side A will be a more normal ending to the game, where the characters talk to you as you help them break something out of the game (or to prevent a breakage) for the good of people.
  • Ch 7 side B will mirror side A, but be about glitching something out of the game.
• Both ch 7a and ch 7b will have the same ending scene, but it will mean different things depending on route.
• My theory leaves a lot of holes that can be filled in by FRIEND, ERAM, and protein. Any place I put them would be guesses with less to go on than what I've already said, though I can imagine places for them that are basically mini boss sized.
  • One of these might be Kris's lost hand.

Okay see you in a few years to see how much I got wrong.