Guide
How the kit works
Start a fight with Miracle Flash when you can. It attacks immediately and, after battle begins, deals Fire DMG equal to 50% of Asta's ATK to all enemies.
Use Meteor Storm to hit a chosen enemy, followed by four hits on random enemies. Each hit deals Fire DMG equal to 50% of Asta's ATK. Astrometry (Talent) grants one Charging stack for each different enemy Asta hits, plus an extra stack for an enemy with Fire Weakness. Repeated hits on the same enemy do not count as hitting different enemies.
Each Charging stack gives all allies 14% ATK, up to five stacks. Starting with Asta's second turn, she loses three stacks at the beginning of each turn. Use Astral Blessing to give all allies 50 SPD for two turns.
Spectrum Beam deals Fire DMG equal to 100% of Asta's ATK to one enemy. Sparks gives it an 80% base chance to Burn the target for three turns; the Burn deals Fire DoT equal to 50% of the Basic ATK's damage at the start of each turn. Ignite gives allies 18% Fire DMG while Asta is on the field, and Constellation gives her 6% DEF per Charging stack.
Build and why
For relics, use four pieces of Messenger Traversing Hackerspace. Two pieces give Asta 6% SPD, and using her Ultimate on an ally with four pieces gives all allies 12% SPD for one turn. Watchmaker, Master of Dream Machinations is an alternative for a team that wants Break Effect: its four-piece effect gives allies 30% Break Effect for two turns when Asta uses her Ultimate on an ally.
For planar ornaments, Broken Keel gives 10% Effect RES and grants allies 10% CRIT DMG when Asta reaches 30% Effect RES. Fleet of the Ageless instead gives her 12% Max HP and gives allies 8% ATK at 120 SPD. Sprightly Vonwacq is another option for Energy Regeneration Rate and an action advance at the start of battle.
Use SPD on the feet and Energy Regeneration Rate on the rope. The recommended body options are HP Percentage or CRIT Rate; for the sphere, choose Fire DMG Boost or HP Percentage. Among substats, look for SPD first, then ATK Percentage, CRIT Rate and CRIT DMG.
Dance! Dance! Dance! is the first Light Cone choice: using Asta's Ultimate advances all allies' actions by 16%. But the Battle Isn't Over gives Energy Regeneration Rate and can recover a Skill Point when her Ultimate targets an ally. Memories of the Past gives Break Effect and regenerates Energy when she attacks. For Fire teammates, Planetary Rendezvous is another option that increases matching-type damage.
Leveling priority
The game's leveling order puts Astrometry first because it supplies the team's ATK buff. Next is Astral Blessing, the source of the team-wide SPD buff.
After those, the listed order is Spectrum Beam, then Meteor Storm. Both deal Fire damage, while the Talent and Ultimate provide the team support that this build focuses on.
To ascend Asta fully, you need 246,400 Credit, 50 Endotherm Chitin, 12 Silvermane Badge, 13 Silvermane Insignia and 12 Silvermane Medal.
For all skills, the listed materials are 2,400,000 Credit, 5 Tracks of Destiny, 12 Harmonic Tune, 54 Ancestral Hymn, 105 Stellaris Symphony, 12 Destroyer's Final Road, 28 Silvermane Badge, 42 Silvermane Insignia and 42 Silvermane Medal.
Eidolons worth it
For Eidolons, I would consider Cosmos Dreams in Calm and Comfort first. It reduces the number of Charging stacks lost each turn by one, making it easier to retain the team ATK buff.
Moon Speaks in Wax and Wane is another useful target: after Asta uses her Ultimate, her Charging stacks do not decrease on her next turn. Aurora Basks in Beauty and Bliss is worth considering for its 15% Energy Regeneration Rate when she has at least two stacks.
Star Sings Sans Verses or Vocals adds one random hit to her Skill, although that hit is not guaranteed to find a different enemy. Meteor Showers for Wish and Want raises Skill and Talent levels, while Nebula Secludes in Runes and Riddles raises Ultimate and Basic ATK levels. You can treat those level increases as less pressing goals than the stack and Energy effects.
Teams
For a damage-over-time team, Kafka and Black Swan are options. Asta can give them her team-wide ATK and SPD buffs, and her Basic ATK can apply Burn. Do not rely on the Burn alone to define the team: its application has an 80% base chance.
Common mistakes
Do not assume every bounce of Meteor Storm gives a separate Charging stack. The extra hits choose random enemies, so they can land on targets already hit. Watch the stack count and make use of enemies with Fire Weakness.
Do not ignore the stack loss at the beginning of Asta's turns. Astrometry (Talent) starts reducing stacks from her second turn, so a full ATK buff will not stay full on its own. Also check the duration of Astral Blessing rather than assuming its SPD buff lasts indefinitely.
Do not forget the thresholds on your ornaments. Fleet of the Ageless needs 120 SPD for its team ATK effect, while Broken Keel needs 30% Effect RES for its team CRIT DMG effect. If you use Dance! Dance! Dance!, its action advance happens when Asta uses her Ultimate.
