His scars, Light-stained eyes, aetherial arm, claws, and, believe it or not, his ear fluff. Because of the nature of his body (it's self-healing and regenerative), wounds don't typically leave a scar when they heal. The exception is magically-inflicted scars and other forces that burrow deep into the skin (e.g. void energy). The scar on his jaw is from his sire, who infused his claws with poison in an attempt to gravely harm Lee. The one across his nose is from Ahri, his ex-turned-voidsent, during their cataclysmic battle in the Burn.

His white/gold eyes are a reminder that he's 1/4 sin eater, which isn't something he likes to remember, despite having accepted it. The aetherial arm is unnerving to some people, especially when his aether overflows and he becomes dangerous to be around. He can accidentally electrocute or burn people with the arm if he isn't managing his aether properly. It can also dissipate when he runs out of aether, and not having an arm at all when that happens isn't something he's used to. He hasn't fully experienced that disability yet.

The sudden growth and sharpness of his claws is a result of fully attuning with Astraliel. He's become mindful of the risk they pose to people and is thankful he can retract them, otherwise he'd avoid touching people at all for fear of hurting them.

His ear fluff is a minor thing, much like how we don't like seeing pimples on ourselves, or body hair, or other natural occurrences in our bodies. The fluff in his ears requires constant trimming and care so it looks neat and clean. If he neglects it, the fur will tangle and grow too long and unruly. His appearance and hygiene mean a lot to him.

It's interesting to discuss these things because while I, and other people, find these traits attractive, sexy, what have you, for the character itself is a different story. I find my thick hair troublesome and ugly sometimes, but people would kill for my hair texture. Things like that. His beauty is meant to contrast the "ugly" that lives inside of him (Astraliel, the Nightcrier), but in the end even the ugly in ourselves is something we must love and accept.