Nicole

5★

PyroCatalystSupport

TL;DR

Nicole's Skill hands the whole party a flat attack bonus and a shield, both for about 20 seconds. Her Burst then makes your on-field character's hits summon little projections that pile in alongside them, in that character's element and off that character's attack. Press both, swap out, and spend the 20 seconds. Build her for attack, because the buff she gives away is a slice of her own.

Rotation

Any other attack buffs in the team go off first.
Skill (E) for the buff and the shield.
Burst (Q), or skip it if the Energy isn't there.
Swap to your damage dealer and spend the 20 seconds.

Abilities

Skill (E)	An attack bonus for everyone nearby plus a shield, both about 20 seconds, with some Pyro damage on the way out. The shield is unusually stubborn against Pyro specifically. About a 16 second cooldown.
Burst (Q)	Costs 60 Energy. For about 20 seconds, whenever the character you're playing hits something, a projection joins in with a free hit in their element that scales off their attack and counts as their damage. Four of those per cast, roughly one every three seconds.

The one mechanic to understand

The buff is a slice of her attack, taken on cast.

What your team gets is a flat attack number worked out from Nicole's own attack at the instant you press the Skill, and it stops growing once she's at about 4,000 attack, which is worth roughly 600 to everyone else. Two things follow from that. Her own gear is the buff, so every attack substat on her is going to your damage dealer. And because it's taken on cast, anything else in the team that raises her attack has to land before she presses the button, not after. Your damage dealer's copy of the buff also grows on its own once they've been on the field a few seconds, which needs nothing from you.

What actually matters

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

Attack in every slot. Sands, goblet, circlet, substats, weapon. The buff and the shield are both percentages of it and nothing else on her sheet does anything.
Energy Recharge only if you want the Burst. Around 160% to 180% if she's your only Pyro character. If reaching that is eating all her attack, drop the Burst and cast the Skill on its own, which is the half that matters.
Her Pyro application is real. Both her buttons put Pyro on the enemy. That's free reactions in some teams and a broken freeze in others, so it's worth knowing before you slot her into a Cryo team.

Gear

A build that works. KeqingMains lists every other option.

Weapon	The highest attack you can find, with Energy Recharge second. Flowing Purity is craftable and is mostly attack.
Artifacts	4-piece Celestial Gift, which is built for her. 4-piece Noblesse Oblige is the easy stand-in and stacks another 20% party attack on top of what she already gives.
Main stats	Attack sands, attack goblet, attack circlet. Energy Recharge on the sands instead if the Burst won't come back without it.

Works well with

Cryo

Hydro

Electro

The attack bonus doesn't care what element anyone is, so she improves nearly any team. Those three are just the reactions her Pyro sets up while she's standing there.

Don't bother

Crit stats. Her own damage is not the product.
Levelling her normal attacks.
Counting on Bennett to get her over the attack cap. Buffs like his raise Nicole's attack but not the number she passes on, so she has to reach it on her own gear.
Forcing the Burst into every rotation when the Skill is up anyway. Uptime on the buff beats an extra four projections.

Want the full theorycrafting version? Read Nicole on KeqingMains.