Guide
How the kit works
If your Burst is ready, start with Dawn. It knocks back nearby opponents, then sends a Phoenix forward. The Phoenix deals Pyro damage along its path and explodes at its destination. Dawn also infuses Diluc's weapon with Pyro.
Use Searing Onslaught for up to three forward Pyro slashes. You can put Normal Attacks from Tempered Sword (NA) between the slashes; don't wait too long to continue the Skill, or it enters cooldown.
After Dawn, keep attacking while the infusion lasts. Blessing of Phoenix extends it by 4 seconds and gives Diluc 20% Pyro DMG Bonus for its duration. Relentless cuts Charged Attack Stamina cost by 50% and extends its duration by 3 seconds, though you can rely on Normal Attacks between Skill casts instead.
Build and why
Four pieces of Crimson Witch of Flames are the first choice. The two-piece bonus gives 15% Pyro DMG Bonus. The four-piece bonus improves several reactions, including Vaporize and Melt, and each use of Searing Onslaught increases the starting two-piece bonus by 50% for 10 seconds, up to three stacks.
Four pieces of Gilded Dreams are another option for a reaction team: after a reaction, the set gives ATK for other Pyro teammates and Elemental Mastery for teammates of different elements. Gladiator's Finale is a third option; its four-piece bonus increases Diluc's Normal Attack damage by 35%. You can also combine two pieces each of Crimson Witch of Flames and Gladiator's Finale.
Use ATK Percentage or Elemental Mastery on the sands, Pyro DMG Bonus on the goblet, and CRIT Rate or CRIT DMG on the circlet. For substats, look for CRIT Rate and CRIT DMG first, then ATK Percentage, Elemental Mastery and Energy Recharge. Elemental Mastery is useful when Diluc triggers reactions.
Wolf's Gravestone is the first weapon choice. It gives 20% ATK and, when a hit lands on an opponent below 30% HP, gives the party 40% ATK for 12 seconds. That party effect can occur once every 30 seconds.
Beacon of the Reed Sea gives 20% ATK for 8 seconds after the Skill hits, with a separate 20% ATK effect after Diluc takes damage. Redhorn Stonethresher is another option: it increases Normal and Charged Attack damage by 40% of DEF.
For a 4-star option, Serpent Spine gains damage stacks while Diluc is on the field, but he takes more damage and loses a stack when hit. Rainslasher is worth considering against opponents affected by Hydro or Electro.
Leveling priority
A suggested order is Searing Onslaught first, Tempered Sword (NA) second and Dawn third. Diluc uses the Skill and Normal Attacks repeatedly during his field time, so both are useful places to invest. Raise the Burst too, since it adds damage and supplies the Pyro infusion.
For maximum ascension, you need 420,000 Mora, 168 Small Lamp Grass, 46 Everflame Seed, one Agnidus Agate Sliver, nine Agnidus Agate Fragment, nine Agnidus Agate Chunk and six Agnidus Agate Gemstone. You also need 18 Recruit's Insignia, 30 Sergeant's Insignia and 36 Lieutenant's Insignia.
To max all three talents, you need 4,957,500 Mora, nine Teachings of Resistance, 63 Guide to Resistance, 114 Philosophies of Resistance, three Crown of Insight and 18 Dvalin's Plume. The talents also require 18 Recruit's Insignia, 66 Sergeant's Insignia and 93 Lieutenant's Insignia.
Constellations worth it
Searing Ember is the standout upgrade in the available rankings. When Diluc takes damage, it gives him 10% ATK and 5% ATK SPD for 10 seconds. It stacks up to three times and can trigger once every 1.5 seconds. Don't take hits on purpose if that puts him in danger.
Flaming Sword, Nemesis of the Dark is worth considering if you reach the final constellation. After Searing Onslaught, the next two Normal Attacks within 6 seconds gain 30% damage and ATK SPD. The Skill also stops interrupting the Normal Attack combo.
Flowing Flame is another upgrade to consider. Two seconds after a Skill cast, the next cast in the combo deals 40% additional damage; that effect lasts 2 seconds. It rewards a slower rhythm, but waiting too long can still let the Skill enter cooldown.
You can stop at C2 rather than pursue the later constellations. Fire and Steel adds three Skill levels, while Phoenix, Harbinger of Dawn adds three Burst levels. Both are useful, but you can leave them alone if you do not want to go further.
Teams
Xingqiu is a Hydro teammate who can contribute from off-field and heal. His element gives Diluc a way to use Vaporize. Furina is another Hydro option listed for Diluc, with off-field presence and healing.
For Melt, consider a Cryo teammate such as Kaeya or Rosaria. Diluc supplies the Pyro attacks; the other element gives those attacks a reaction to work with. Crimson Witch of Flames supports both Vaporize and Melt.
An Anemo slot such as Kaedehara Kazuha or Sucrose can bring Swirl. Zhongli offers a shield, while Xianyun is an Anemo healer. One team to try is Diluc, Xingqiu, Kaedehara Kazuha and Bennett; Bennett adds another Pyro character, and Xingqiu provides healing.
Common mistakes
Don't leave too much time between uses of Searing Onslaught. Once it enters cooldown, you lose the remaining slashes from that sequence. At C4, practice the slower timing without letting the combo expire.
Don't assume Diluc always has Pyro on his weapon. Dawn (Q) provides the infusion, so use the infused window for attacks and watch for it ending.
Don't build only for one part of his kit. Pyro DMG Bonus helps his Pyro damage, while CRIT stats and ATK support his attacks. Choose Elemental Mastery when the team lets Diluc trigger reactions, and remember that Serpent Spine loses a stack when he takes damage.
