Key of Khaj-Nisut is the closest fit on the game's own numbers: Kuki Shinobu's kit multiplies HP, and a weapon is ranked here on whether its ascension stat and its passive act on that stat. Primordial Jade Cutter, Serenity's Call and Splendor of Tranquil Waters come next. No playtested ranking has been imported for Kuki Shinobu, so this is arithmetic over the kit data rather than a damage measurement.
Run Thundering Fury on Kuki Shinobu, with Vourukasha's Glow and Song of Days Past behind it. Main stats are HP% sands, HP% goblet, Healing Bonus circlet. Roll substats in the order Energy Recharge > HP% > CRIT Rate > CRIT DMG.
Talent priority is Elemental Burst > Elemental Skill > Normal Attack. The Elemental Burst costs 60 energy, which is what an Energy Recharge target has to clear.
The strongest team is Nahida, Xingqiu, Yelan and Kuki Shinobu, built around Kuki Shinobu: Electro · Hyperbloom.