OK so:
You know how every chapter has it's theme? For example, how chapter 4's theme is fate and chapter 3's is nostalgia? Well, I've seen quite a few people misunderstanding chapter 5's theme, so I'm here to give what I believe it is.
Short answer: it's a flawed perception of the past.
Long answer: we all know that chapter 5 is based off of chapter 1. But, in a way, it's also the opposite of some things. Here, I'll give all my evidence to support this.
Music: both garden of hopes and dreams and the rude buster variant (idk the name) are just remixes of the og popular enough to get in the game.
Areas: in chapter 1, the cliffs (the first area in the game, I think that's what it's called) is very minor and doesn't have too much importance. In chapter 5, it is one of the 3 main areas of the entire chapter.
Jail: in chapter 1, the jail scene is a very big and important scene for susie, and treated very seriously. In chapter 5, it is the exact opposite; a short gag. Also, eating the moss is optional in 1 but necessary in 5.
Jevil: Jevil is rarely mentioned in chapter 1, but chapter 5 has many, many mandatory things referencing him.
Castle: chapter 1's catsle is very short, while chapter 5's Castle has 2 whole areas of the chapter dedicated to it
King: King in chapter 1 is only seen at the near end of it, while Asgore in chapter 5 is shown many times in the dark world.
The chapter is perceiving the past in a completely different way, making things seem more lighthearted than it actually is.
There's probably some more evidence, but this is what I have for now. If I find more, I'll put it here.
