Guide
How the kit works
Before a fight, use The One True Sword when you can. For the first 2 turns of the next battle, Yanqing deals 30% more DMG to enemies whose current HP is at least 50%.
In battle, use Darting Ironthorn on your target to deal Ice DMG equal to 220% of Yanqing's ATK and activate Soulsteel Sync for 1 turn. One With the Sword makes him less likely to be attacked while the effect is active and gives him 20% CRIT Rate and 30% CRIT DMG.
After an attack during Soulsteel Sync, there is a 60% fixed chance of a Follow-Up ATK. It deals Ice DMG equal to 50% of ATK and has a 65% base chance to Freeze the target for 1 turn. A Frozen target cannot act and takes Ice Additional DMG equal to 50% of Yanqing's ATK at the start of each turn.
Use Amidst the Raining Bliss while Soulsteel Sync is active when possible. It gives Yanqing 60% CRIT Rate and, with Soulsteel Sync, another 50% CRIT DMG for 1 turn before dealing Ice DMG equal to 350% of ATK. Frost Thorn deals Ice DMG equal to 100% of ATK, but it does not activate Soulsteel Sync.
Build and why
For relics, start with four pieces of Scholar Lost in Erudition. It gives 8% CRIT Rate and increases Skill and Ultimate DMG by 20%. After an Ultimate, it also increases the next Skill's DMG by 25%, matching Yanqing's frequent use of that attack.
Hunter of Glacial Forest is the next option: it gives 10% Ice DMG and, after an Ultimate, 25% CRIT DMG for 2 turns. The Wind-Soaring Valorous is another option. Its four-piece bonus gives 6% CRIT Rate and, after a Follow-Up ATK, 36% Ultimate DMG for 1 turn. The Follow-Up ATK is chance-based, so plan around that condition.
For planar ornaments, consider Firmament Frontline: Glamoth for ATK and extra DMG at 135 or 160 SPD. Inert Salsotto gives CRIT Rate and increases Ultimate and Follow-Up ATK DMG when current CRIT Rate reaches 50%. Space Sealing Station is an ATK option with an extra bonus at 120 SPD.
Use CRIT DMG on the body, SPD on the feet, Ice DMG Boost on the sphere and ATK Percentage on the rope. For substats, look for CRIT Rate, then CRIT DMG, ATK Percentage and SPD. Remember that Soulsteel Sync and the Ultimate already give a combined 80% CRIT Rate while both are active.
In the Night is the first weapon choice. It gives 18% CRIT Rate and rewards SPD above 100 with more Basic ATK and Skill DMG and more Ultimate CRIT DMG. Sleep Like the Dead gives 30% CRIT DMG and a conditional CRIT Rate boost. Swordplay is an option when Yanqing keeps hitting the same target: its DMG stacks disappear when he changes targets.
Leveling priority
Level Amidst the Raining Bliss first for Yanqing's single-target Ultimate damage. Follow with Darting Ironthorn, then One With the Sword. Leave Frost Thorn until last: the Skill is the attack that activates Soulsteel Sync.
For maximum ascension, you need 308,000 Credit, 65 Gelid Chitin, 15 Thief's Instinct, 15 Usurper's Scheme and 15 Conqueror's Will.
To level all skills to their maximum, prepare 3,000,000 Credit, 8 Tracks of Destiny, 18 Arrow of the Beast Hunter, 69 Arrow of the Demon Slayer, 139 Arrow of the Starchaser and 12 Guardian's Lament. You also need 41 Thief's Instinct, 56 Usurper's Scheme and 58 Conqueror's Will.
Eidolons worth it
As a suggested order for Eidolons, consider Swift Swoop, Supine Serenade and Searing Sting. Swift Swoop extends active Soulsteel Sync or Ultimate buffs by 1 turn when an enemy is defeated, so its value depends on getting that defeat while the buffs are active.
Supine Serenade adds 10% Energy Regeneration Rate while Soulsteel Sync is active. Searing Sting gives 12% Ice RES PEN when Yanqing's current HP is at least 80%, making his HP relevant to that bonus as well as his survival.
Svelte Saber adds Ice DMG equal to 60% of ATK only when Yanqing attacks a Frozen enemy, so it is not a necessary stopping point by itself. Sword Savant and Surging Strife raise skill levels; stopping before them is reasonable if you do not want to pursue further Eidolons.
Teams
Give Yanqing a sustain teammate and try to prevent him from receiving DMG. Gepard is an Ice Preservation option listed for him. Keeping Soulsteel Sync active lets Yanqing retain its CRIT bonuses and chance of a Follow-Up ATK.
For a buffer, consider Wind Harmony character Bronya or Lightning Harmony character Tingyun. Ruan Mei is another listed buffer if you want another Ice character. Yanqing contributes focused Ice damage, with a chance to Freeze from his Follow-Up ATK.
A debuffer such as Silver Wolf is another option. Her Quantum element also gives the team a different combat type from Yanqing's Ice. Pick the remaining roles around the enemies and the protection Yanqing needs.
Common mistakes
Do not assume Soulsteel Sync stays active after Yanqing receives DMG. Use Darting Ironthorn to activate it again, and check for the effect before relying on the Ultimate's extra CRIT DMG.
Do not build CRIT Rate without accounting for the 20% from Soulsteel Sync and 60% from the Ultimate. Those bonuses do not have identical conditions, so also consider how much CRIT Rate Yanqing has when the Ultimate buff is absent.
Do not count on every attack producing a Follow-Up ATK or Freeze. The Follow-Up has a 60% fixed chance, and its Freeze has a separate 65% base chance. This matters when using The Wind-Soaring Valorous or relying on Svelte Saber.
