okay so i was wrong about the "he realized there are no good people" cause he knows there are but i think my guess besides that part was mostly right 

i don't know i LOVED this and rereading it i definitely understood it more than when i first read it and i loved it. they didn't understand their hatred or the malice they carried in their heart from the people around them and when they were separated after the first incident i'm pretty sure that's when as time went by yeonwoo accepted that malice in his heart and listened to the reflection but jun on the other hand "changed" and ignored the malice and reflection hence him making himself forget everything but them reconnecting slowly made him realize what it was that they both felt as children and in the end accepted that part of himself instead of shutting it out.
my only complaint is i wish they would explain how yeonwoo and the house caused those deaths like what connected it all but besides that i loved every part of this 10/10

this is just my opinion but i think jun realized that there are truly no good people in the world and that people are only nice to get what they want and the reflections are telling them that they need to be stronger in order to take what they want from the cruel world and if they are apart they aren't strong but if they're together they are stronger and only they can give each other what they want if they do it together

i feel like the mirrors are how they truly are but they're trying to suppress that part of themselves (as kids) and as yeonwoo got older he accepted that part of himself and jun wanted to be a "good person" and ignore that part of himself and chuck them off to be hallucinations(when his reflection would speak to him) but now that they're together again jun slowly let the mask fall off of being a "good person" and realized that "yeah i only need yeonwoo and no one else, i don't care about anyone else" 
it might've been obvious but i like fully just put it all together myself lol

holy shart

jesus

um.. what was that

yep rip everyone

oh no... i don't like this

omg 

NO

oh no i feel like that was a bad idea

bruh we all knew

wait why i kinda fw it