So while not an official, canon, post. Here’s what I would do.
Assuming you are looking at early adult, late teen Jhin. He was already a monster then Cause...
Jhin started training super-young (4). By the time he was a tween in d&d terms he was already a pretty decent level Kensei Monk. (From Xanthar’s Guide) (At least lvl 5, prob much, much higher) .
You can use that class as a baseline or starter— however as a child Jhin should probably start lvl 1 as a sorcerer (wild magic) then become a Kensei monk for 5 levels. Then multiclass again into fighter for 2 levels and then yet again into rogue for at least 6 levels.
Jhin’s dad specialized in daggers and darts— not swords. His father’s school was all about attack speed— think a ranged attack storm of daggers. BUt Jhin hated his dad, so while Jhin was trained to attack fast, he chooses not too.
Only in his adulthood does he move into a bard class — though his magic is spirit and nature based (So i would look for spells bards share with Druids).
He’s probably lawful evil. He’s the kinda guy who would be very upset by someone failing to follow even some minor social norm— but personally believes he is above the law.
His stats... hmmm.
This will be hard with a point buy system.
Start with max wisdom.
Then high intelligence.
Dex is only “average” at the start. (But he trained a lot, so your advancements will go here—cause Jhin’s lack of natural agility was a huge dissappointment to his dad)
Strenght and Constitution are your dump/garbage stats.
Lastly, charisma is “good”, so you should start it at the min for the bard/sorcerer class (13?).