Guide
How the kit works
Before combat, Fiery Queller creates a Special Dimension for 15 seconds. Entering battle with enemies inside it deals Fire DMG to all of them and has a 100% base chance to apply one Ashen Roast stack. Only one allied Special Dimension can exist at a time.
Quartet Finesse, Octave Finery gives Jiaoqiu a 100% base chance to apply a stack whenever his Basic ATK, Skill or Ultimate hits an enemy. One stack makes that enemy take 15% more damage; each later stack adds 5%, up to five stacks. Ashen Roast lasts two turns and deals Fire DoT equal to 180% of Jiaoqiu's ATK at the start of each turn.
Use Scorch Onslaught to hit a main target and adjacent enemies. It has a separate 100% base chance to apply a stack to the main target. Heart Afire hits one enemy and can apply a stack through the Talent.
Pyrograph Arcanum first sets every enemy's stacks to the highest count on the field, then damages all enemies and creates the Zone. Enemies inside take 15% more Ultimate DMG. When an enemy acts, the Zone has a 60% base chance to apply a stack, up to six triggers per Ultimate and once per enemy per turn.
The Zone lasts three of Jiaoqiu's turns and disappears if he is knocked down. While it is active, Seared Scent applies Ashen Roast to enemies entering combat, matching the highest stack count present, with a minimum of one.
Build and why
For relics, use two pieces of Messenger Traversing Hackerspace with two pieces of Sacerdos' Relived Ordeal for SPD. A four-piece Eagle of Twilight Line is another option: its Wind DMG bonus does not help this Fire character, but its four-piece effect advances his action by 25% after his Ultimate.
For planars, Sprightly Vonwacq gives Energy Regeneration Rate and, at 120 SPD, advances Jiaoqiu's first action. The game's build also recommends Prisoner in Deep Confinement for ATK and damage against enemies with DoT, plus Pan-Cosmic Commercial Enterprise for Effect Hit Rate and ATK.
Choose Effect Hit Rate on the body, SPD on the feet, Fire DMG Boost on the sphere and Energy Regeneration Rate on the rope. For substats, follow Effect Hit Rate, ATK Percentage, then SPD. Hearth Kindle gives 60% ATK for every 15% Effect Hit Rate above 80%, up to 240% ATK.
Those Many Springs is the first weapon choice. It gives 60% Effect Hit Rate and can apply Unarmored, making its target take more damage. Lies Dance on the Breeze gives SPD and can apply Bamboozle to reduce enemy DEF. Incessant Rain gives Effect Hit Rate and can apply Aether Code, which increases the target's damage received.
Leveling priority
Follow the game's order: Quartet Finesse, Octave Finery, Pyrograph Arcanum, Heart Afire, then Scorch Onslaught. The Talent controls Ashen Roast and its Fire DoT, while the Ultimate spreads stacks and creates the Zone. Basic and Skill can both apply stacks through the Talent.
For maximum ascension, gather 308,000 Credit, 65 Raging Heart, 15 Immortal Scionette, 15 Immortal Aeroblossom and 15 Immortal Lumintwig.
For all skills, gather 3,000,000 Credit, 8 Tracks of Destiny, 18 Fiery Spirit, 69 Starfire Essence, 139 Heaven Incinerator and 12 Regret of Infinite Ochema. You also need 41 Immortal Scionette, 56 Immortal Aeroblossom and 58 Immortal Lumintwig.
Pyre Cleanse is worth unlocking too: it gives Jiaoqiu 15 Energy immediately when battle starts.
Eidolons worth it
Pentapathic Transference is a good first upgrade to consider for team damage. Allies deal 40% more damage to enemies with Ashen Roast, and applications through Quartet Finesse, Octave Finery add one extra stack.
From Savor Comes Suffer is worth considering if you want more damage from Jiaoqiu's DoT. It increases the Fire DoT multiplier against enemies with Ashen Roast by 300%.
Nonamorphic Pyrobind is a later option: it raises the stack limit to nine, transfers stacks when an enemy is defeated and reduces All-Type RES by 3% per stack. Leisure In, Luster Out instead reduces enemy ATK by 15% while the Zone exists.
If you are happy to stop earlier, Flavored Euphony Reigns Supreme and Duel in Dawn, Dash in Dusk are reasonable upgrades to leave for later: they raise skill levels rather than adding a separate effect.
Teams
Acheron is a strong teammate option for a team that wants debuffs and increased Ultimate DMG. Jiaoqiu's Zone increases the Ultimate DMG enemies receive, while Ashen Roast makes them take more damage in general.
Common mistakes
Do not treat a 100% base chance as a guaranteed application. Build Effect Hit Rate and check whether Ashen Roast is actually on the target before relying on its damage increase.
Do not overlook the Zone's limits. Its stack effect can trigger up to six times per Ultimate, and it disappears if Jiaoqiu is knocked down. Keep him alive and use the Ultimate to refresh the trigger count.
Do not equip four pieces of Messenger Traversing Hackerspace expecting its team SPD effect from Jiaoqiu's Ultimate. That effect requires an Ultimate used on an ally; Jiaoqiu's Ultimate damages enemies instead. Two pieces are useful for their SPD.