Kinich

5★

DendroClaymoreMain Damage

TL;DR

Kinich hooks a grapple line onto an enemy and swings round them for about 10 seconds. While he's up there his attacks fill his nightsoul meter, and when it's full his Skill becomes one enormous Dendro cannon shot. You want to fire that cannon four or five times per swing, and the thing that lets you is a Pyro teammate keeping the enemy on fire.

Rotation

Pyro teammate gets the enemies burning. Someone in the team wears 4-piece Deepwood Memories.
Kinich: hold Skill (E) to grapple on.
Normal attack twice, then tap Skill (E) for the cannon.
Burst (Q) once for the dragon, then keep repeating two attacks and a cannon until the state drops.

Abilities

Skill (E)	Hold it to grapple onto a nearby enemy, which starts his 10 second state. Once he's up there, tapping it again fires the cannon, provided the nightsoul meter is full.
Normal attacks	While grappled these become Dendro shots that circle the target. They fill his nightsoul meter, and they count as skill damage for artifact purposes.
Burst (Q)	Summons a little dragon that keeps breathing Dendro on things, and adds a couple of seconds to his state. 70 Energy.
His nightsoul meter	Fills on its own while he's grappled, faster from his attacks, and fastest from burning damage on the enemy. The cannon spends all of it.

The one mechanic to understand

The green circle on the ground.

Every time you grapple or fire the cannon, a green patch appears on the floor nearby. Swinging through it hands you a chunk of nightsoul meter for free, a bit more than an attack gives you, and it costs no time because you were swinging anyway. You often catch one without trying, but if you can see it, steer through it.

What actually matters

The two or three real decisions. Everything else is noise.

He needs Pyro, not for the reaction but for the meter. Burning damage refills his nightsoul meter faster than anything else he can do. Without a Pyro teammate he fires the cannon once or twice and the character stops being interesting.
Someone has to wear Deepwood Memories. The 4-piece cuts enemy Dendro resistance by 30%, and since all his damage is Dendro that's a straight 30% more damage. Put it on the Pyro support, not on him.
He needs a target to grapple. No enemy in range, no state, no cannon. Against a single enemy that dies early you can be left standing on the ground mid-rotation.
Skipping the Burst is fine. Casting it every rotation wants a painful amount of Energy Recharge. Most people cast it when it's there and don't build for it.

Gear

A build that works. KeqingMains lists every other option.

Weapon	Crit, then attack. Earth Shaker is craftable in Natlan and its bonus is live the whole time the enemy is burning, which is the whole rotation.
Artifacts	4-piece Obsidian Codex. A big slab of crit rate and damage while he's in his state, which is the only time he does anything.
Main stats	Attack sands, Dendro damage goblet, Crit circlet. Energy Recharge only if you've decided you want the Burst every time.

Works well with

Pyro

Hydro

Pyro is mandatory. Hydro as a fourth turns the burning into Burgeon, which is more damage and more mess. A second Dendro character is also fine if you just want the resistance shred somewhere.

Don't bother

His ground-level normal attacks. You are never using them in a fight.
Elemental Mastery. His damage is direct Dendro, not reactions.
Bringing a healer who needs you to stand still. He's on a rope, that doesn't work.

Want the full theorycrafting version? Read Kinich on KeqingMains.