heres something I noticed a while ago. In Undertale it's started, more than once I think, that stripes are only worn by children. At the time I wasn't sure whether Kris was in middle or high school. But then it hit me. None of their classmates are wearing stripes. Even Temmie, who in Undertale wears stripes, didn't in Deltarune. This fact is a great example of their regression. They refuse to grow up and let go. so they use age regression as a coping mechanism?
oh, and adding on, so does Susie. she wears a blue shirt with a white stripe on it. But it's hard to see because of her jacket. It may symbolise that Susie, deep down, acts like a child, or is a child mentally because of how no one else ever bothered to take care of her and let her grow as a person. Think abut it. There's a lot of hints she was abused and/or neglected by her own family. But the jacket symbolises how she tries to hide that from everyone, by being the "school bully". It represent her insecurity, trying to not let anyone know about who she truly is. May explain why she suddenly lashes out at Kris when they witness her eating chalk.
This is what makes Susie and Kris different. Kris is dwelling in the past, wanting to be the child who was happy with a family that's whole (but asgore is divorced). But everyone can see Kris' immaturity and calls them a "kid", because he pranks the others and stuff. Susie on the other half, tries to conceal it and make sure nobody sees that.
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guys from now on i'll call kris a they/them