1) Kyle owns few things. He doesn't get attached to physical possessions, and carefully crafts his living spaces with the same utilitarian severity that he applies to his all-black wardrobe. The only thing he cares about in this world is his collection of original press Joy Division vinyl. His feelings about Ian Curtis are equally intense, so don't ask.
2) Kyle has full sleeve tattoos on both arms, based on the lush nature scenes of Joseon period paintings. As a child he was never much of a fan of the arts, always much more interested in academic pursuits, but his mother Soon-bak was. She owned numerous prints of reproduced Ahn Gyeon and Hyewon works, among extensive examples of French impressionism and Italian futurism. After his parents died when Kyle was six, his aunt kept the prints; while Kyle doesn't have access to them anymore, the tattoos are a reminder of his mother.
3) Amanda Sidhari was the only woman Kyle ever truly loved. He always planned to marry her; if he hadn't gone to prison, he would have proposed. But he did go to prison, and their relationship blew apart. It's easier to blame it on his mistakes, but she had no intention of marrying him, even before prison. He still doesn't know that. Amanda hasn't had the heart to tell him so. She doesn't know if it matters anymore.
4) Douggie is Kyle's blind spot in every conceivable way. After his parents died, his aunt and uncle tasked him with stepping up to look after his younger cousin, and ever since Douggie has been his number one priority. But because Douggie knows Kyle will always be there to bail him out, whether it's a fight or a bad loan or a night in jail, Douggie's never had to take care of himself. Even after everything that's happened, Kyle will always feel responsible for him. The problem is people like Ricky Nang and Raymond Gho know this, and this will eventually be used against Kyle in a big way.
5) While there are a wide range of unique powers seen across The Crashers universe, Kyle's invulnerability is possessed by another character. This character appears in every book but isn't revealed to be powered until the fifth installment. Their mirrored abilities will eventually draw Kyle and this character together in strange, potentially dangerous ways.
6) Kyle will never admit it in public, but the collected works J.R.R. Tolkien is his jam of jams. Once Clara discovers this, the fandom wars begin.