Dustyn
Backstory and facts below the cut
Backstory:
He mostly follows the canonical story (in game)
He breaks at the same point as Kilzy did, except his breaking point was reached with genocide routes (of which he remembers everything. Everyone remembers everything in ST). He eventually lost it, abandoning all reason in his frenetic attempts to stop the murderous child. He eventually says to his dad "what if I just kill everyone before them!? They'll get bored!! And leave!" gaster couldn't explain that if they leave they wouldn't reset in time. He went on with his plan, laughing maniacally as he fulfilled it. He killed everyone. Even his dad.
He eventually regained his mind, entering a profound depression and crisis. After years he eventually desensitized to it and got somewhat better
Facts:
He lives with Kilzy, considers him as a brother, and cannot see himself living without that annoying cheese ball.
He will never admit it but he actually kinda likes kilzy's teasing.
Never drinks.
He smokes
Hates unnecessarily loud noisy people with the exception of a few people
His brother doesn't haunt him. In fact, everyone else but his brother visit him from time to time. The reason is that his brother wasn't killed by him, but died protecting him
The ghost that stays with him the most is Synster, his dad/mother. Her name is now Phantom, and unlike classic dust, phantom actually guides him and tries to help him as much as she can