Let's start with runes.
I've always felt at home bringing Fleet Footwork on Jhin because of his lack of mobility. If you bring Fleet Footwork you have a much smoother time in lane because of the sustain it gives you, and it's a lot easier to run away or engage, whichever is needed at the time. Same goes with celerity. You have no dashes or leaps on jhin so you have to rely on your movement speed from runes, and your crits. Celerity makes it easier to move around the map, and gives you a few extra AD. Coup de grace is a must have on jhin because he has his own version of coup de grace in his kit with his passive! "The fourth attack is guaranteed to critically strike, dealing 15 / 20 / 25% of the target's missing health as bonus physical damage." This just increases his burst damage for squishies and his dueling potential.

Jhin's passive Whisper is important because it's what his entire kit revolves around. It's simple really. You have four shots in the chamber, and instead of gaining attack speed from items, it shifts the attack speed into extra attack damage. Which is why some people build over other boots even though Jhin has a fixed attack speed. Every fourth fourth shot while still in combat will be a critical strike dealing 175% of Jhin's total attack damage and granting him 4% movement speed increased even further based on the amount of extra attack speed Jhin has. also increases his total attack damage by 4-44 percent based on level. It's a lot of extra damage, and when used correctly, you can be a weapon of mass destruction.

Jhin's Q scales with 40 / 47.5 / 55 / 62.5 / 70 percent of his AD per level so it's nice to have a little extra oomph for the early lane pressure and an easier time farming. On thing that's important to note is that, Jhin's W when used to root an enemy champion, not only slows down the enemy champion, but also gives you movement speed equal to that of the fourth crit from your passive. So if you can spare a second to throw your W behind you without getting caught, you get a small speed boost. Jhin's E Captive Audience reveals enemies who are camouflaged for four seconds, so you can use that to your advantage in lanes with and
Finally, Jhin's ultimate: Curtain call is a long range version of his passive! four shots total, with the last one being a crit. What's different is that Curtain call's final shot critically strikes for 200% damage. Unaffected by the damage reduction in Jhin's passive.

There are a few things you need to remember when buying items for jhin. You have zero mobility in your kit besides the movement speed from your passive. And you do a sh*t ton of damage. Now, if you buy items that help you move around the map faster, and burst fools, than you're playing the game how it's supposed to be played. This is why i recommend Youmuu's Ghostblade as an early purchase.
Duskblade of Draktharr, Lord Dominik's Regards, and Death's dance, are all for raw damage.

You can replace with if you want more damage, but the movement speed is better in most cases, since you deal crazy damage without

You can also replace with if you prefer the extra range and movement speed, but the attack damage and true damage it adds is very important to your burst potential.

This is my first attempt at a guide so I apologize if it's not up to your standards, but I would love to get there! Constructive Criticism is greatly appreciated, and I have no doubt I will make this guide better and more in-depth in the future, but for now... Thank you for reading, and I hope you have a great day! :)

p.s.

is secret op on jhin