As I've played jhin I've listened to his quotes to try to understand his character/mind. I feel like he isn't as happy as he'd like to convince himself he is. The visceral joy of killing he lives for becomes clouded and distant when he's away from combat. It reminds me a lot of Sion and how he goes from a raging warlord in combat to someone almost in a fugue state. Jhin is much the same way in his ponderings.
Personally, I feel like he rationalizes his behavior as performance and art, something otherwise desirable, because he can't come to terms with the monster he is. He distances himself from his victims to view them as objects - as works of art, a performance, or puppets - to make it easier for him to do what he does. Objectification isn't unheard of in serial killer behavior. I'm not an expert on criminal or abnormal psychology or anything but from what I do know about it that's what I think, personally.
It's been said elsewhere, but I feel like he alludes to the fact that he realizes he can't control his psychopathic behavior in his VO. Plus there's the shattered mirror in his splash art kind of hints to this as well. Jhin is a crack shot, he wouldn't hit it unless he aimed for it. Everything about his "performances" must be perfect, so why shoot a mirror? I remember a riot poster saying that he wouldn't like to look himself in the mirror.
Here are some quotes from his VO that I feel illustrate it:
"This art is a compulsion. I cannot resist it."
"There is nothing for me but this."
"I always say every performance is the last, but I lie every time."
"I am a slave to this passion."
"Watch my puppets dance."
"They're puppets. I pull their strings, and then they dance."
"I never hurt anyone. It is the performance that kills."
"The face of your killer is identical to mine."
"I'm misunderstood. Beauty can't be evil."
In these quotes, I feel like he demonstrates objectification of his victims and dissociation from what he does. HE cannot be the killer, because he can't accept that he is a murderer, though he will readily admit that he kills for art. To him they're two different things.
"My work asks questions, it never has answers."
This last quote makes me wonder if while "working", Jhin asks himself questions about himself that he can't find an answer for, which could possibly also support the notion that Jhin, in his more lucid moments, is a very troubled person.
when he finishes his performance he's happy af...
makes me happy
isn't still saying super-happy things. Really, they need subtitles for her so we can all have our days brightened by her positivity.
mini gnar
and 
is coming.
