Kazuha is a wanderer, and his usability reflects this. Despite his flexibility, he doesn’t truly enable certain compositions. He’s just good in any composition, making Kazuha a great character to Wish for especially if you’re free-to-play or a light spender.
The obvious choice for Kazuha is to slap a four-piece Viridescent Venerer on him and call it a day, but he can actually use all those “B-Side” artifacts you get like Lavawalker or Thundersoother.
If you’re using Kazuha as a mixed DPS/support, you’ll want ATK% on his Sands, Anemo DMG Bonus on the Goblet and CRIT DMG, CRIT Rate or Elemental Mastery on his Circlet. If he’s pure support, get Elemental Mastery across the board to maximize his team buff.
Kazuha can have some issues with Energy Recharge, so getting that on sub-stats is ideal.
4 Viridescent Venerer
Four pieces of Viridescent Venerer will give you a 60% damage bonus to Swirl, while lowering the resistance of enemies when you Swirl an Element. Kazuha’s Elemental Skill, Chihayaburu, can absorb any Elements Swirled and deal that damage on the plunge. With that in mind, you can use some truly unusual sets on Kazuha.
4 Thundersoother or 4 Lavawalker
You know when you grind for Thundering Fury or Crimson Witch and you get good stats but it’s for the wrong set? This is where they can go. The two-piece bonuses from either of these give resistance, but a full four-piece suite gets you a damage bonus against enemies affected by their respective Element.
That’s not an Elemental DMG bonus: it’s a full, no restrictions damage bonus against enemies affected by Electro for Thundersoother and Pyro for Lavawalker. In the right teams, this enables Kazuha to act as an extraordinarily powerful mixed DPS/Support unit.
The only catch is that it specializes Kazuha into a certain team composition. Obviously, a Thundersoother set for Kazuha makes him work best with Electro characters like Fischl and Beidou and a Lavawalker set works best with Xiangling and Bennett.
2 Viridescent Venerer/2 Bloodstained Chivalry or 2 Pale Flame
If you want to use Kazuha as a main DPS, you can use just two Viridescent Venerer to get the Anemo DMG bonus and two of either Bloodstained Chivalry or Pale Flame (they have the same two-piece bonus). This just boosts his power in general, giving some extra punch to his Skills and to his Normal Attacks.
Luckily, one of Kazuha’s best weapons is craftable. Combined with his versatility in battle, this allows Kazuha to be a a great free-to-play friendly unit if you manage to score him. Since Kazuha gives a bonus based on his Elemental Mastery, the Iron Sting is the F2P go-to. The Iron Sting gives a DMG bonus after dealing Elemental DMG, synergizing well with his Elemental Burst.
Energy Recharge won’t be wasted, so Sacrificial Sword, Favonius Sword or Festering Desire are also great choices especially if you build Kazuha as a main DPS or mixed support.
If you have any of the five-star weapons, throw them on him. The raw stat increase makes any five-star Sword great on him.
My only lament? There is no katana in the game to give him.