Sayu build recommendations
Sayu does more damage with EM builds and heals more with ATK hybrid builds, Healing Bonus hat can be used for better heals while maintaining respectable damage. Note that Sayu wants a large amount of energy recharge when used as the only anemo slot on the team (200%ish).
Regarding Weapon Choices
Wolf's Gravestone is a universal claymore that is capable of buffing your teammates along with providing more healing in Sayu's case. It is best used once you achieve your ER threshold.
When used in its niche with aggravate teams it can outpeform . Outside of that its just a energy% stat stick.
Regarding Artifact Sets
The bread and butter artifact set for Anemo units, this set provides the ability to shred the enemy's elemental resistance while also buffing Sayu's swirl damage output.
Artifact stats priority
er em atk%