Guide
How the kit works
Start with Vindication when Danjin enters, or use the attacks from Execution. After the second Basic Attack, or after her Intro Skill, use Crimson Fragment twice to perform Crimson Erosion (Skill). Its second strike applies Incinerating Will when it hits, increasing Danjin's damage against that target by 20%.
After the third Basic Attack, use Crimson Fragment up to three times for Sanguine Pulse (Skill). Overflow (Passive) gives Danjin 30% Heavy Attack DMG for 5 seconds after Sanguine Pulse, making that a useful time to spend Ruby Blossom.
Crimson Fragment gives Ruby Blossom, but each attack consumes 3% of Danjin's max HP. When her HP is below 1%, it stops consuming HP. With at least 60 Ruby Blossom, hold Basic Attack to use Chaoscleave (Forte), which deals Heavy Attack DMG and heals Danjin. Follow it with a Basic Attack for Scatterbloom (Forte).
After a successful Dodge Counter, Crimson Fragment can trigger Crimson Erosion. Crimson Light increases that version's damage by 20% and doubles both its HP cost and Ruby Blossom gained. Use Crimson Bloom for its Havoc attacks, then Duality when you want to pass 23% Havoc DMG Amplification to the incoming character for 14 seconds or until they switch out.
Build and why
Moonlit Clouds is a guide-listed option if you want Energy Regen: its two-piece effect gives 10%. Havoc Eclipse is the game's five-piece option and its two-piece effect gives 10% Havoc DMG, which suits Danjin's attacks. The supplied description does not state either set's five-piece effect.
Blazing Brilliance is the leading weapon choice in the guides. It gives 12% ATK, and its Searing Feather stacks grant Resonance Skill DMG Bonus. Casting a Resonance Skill grants five stacks, so Danjin can build them through Crimson Fragment.
Red Spring is the next option. It gives 12% ATK and builds Basic Attack DMG Bonus when Danjin deals Basic Attack DMG. Emerald of Genesis follows: it gives Energy Regen and grants ATK stacks when she casts her Resonance Skill.
For a 4-star option, Lumingloss gives Basic Attack DMG Bonus and Heavy Attack DMG Bonus after a Resonance Skill, fitting both her normal attacks and Chaoscleave (Forte). Commando of Conviction gives ATK after Vindication. Endless Collapse gives Resonance Energy and ATK after a Resonance Skill, with a 20-second trigger interval.
ATK, Crit. Rate and Havoc DMG are useful stats to consider for her damage. Energy Regen is another option if you want to use her Liberation more often; balance it against the damage stats you want.
Leveling priority
A suggested order is Serene Vigil first, followed by Crimson Fragment, Crimson Bloom, Execution and Vindication. Serene Vigil contains Chaoscleave and Scatterbloom, while Danjin uses Crimson Fragment repeatedly to build Ruby Blossom.
For maximum character ascension, you need 170,000 Shell Credit, 4 Crude Ring, 12 Basic Ring, 12 Improved Ring, 4 Tailored Ring, 46 Strife Tacet Core and 60 Belle Poppy.
For all skills, you need 2,030,000 Shell Credit, 25 Crude Ring, 28 Basic Ring, 40 Improved Ring, 57 Tailored Ring, 26 Dreamless Feather, 25 Inert Metallic Drip, 28 Reactive Metallic Drip, 55 Polarized Metallic Drip and 67 Heterized Metallic Drip.
Resonance Chain nodes worth it
Dusted Mirror (Sequence 2) is a good upgrade to consider first: Danjin deals 20% more damage when attacking a target affected by Incinerating Will. You still need to land the second strike of Crimson Erosion (Skill) to apply the mark.
Solitary Carnation (Sequence 4) gives 15% Crit. Rate when Danjin has more than 60 Ruby Blossom. The effect stays until the end of Scatterbloom (Forte), even after Chaoscleave (Forte) consumes the resource. Bloodied Jade (Sequence 6) is also worth considering for teams: Chaoscleave gives all team members 20% ATK for 20 seconds.
Fleeting Blossom (Sequence 3) can be a lower priority if you prefer the bonuses above, since it gives 30% Resonance Liberation DMG Bonus rather than a bonus to Danjin's other attacks. These priorities are suggestions; the supplied guide evidence does not rank her sequences.
Teams
Pair Danjin with a Havoc damage dealer who can use Duality. Rover: Havoc, Camellya and Phrolova are named as teammates in the guides. The incoming character gets the 23% Havoc DMG Amplification, so plan to keep that character on the field while using it.
A sustain slot is worth considering because Danjin spends HP during her rotation, even though Chaoscleave (Forte) heals her. Verina and Baizhi are also named as teammates in the guide evidence. Danjin can contribute her own damage before passing the Outro boost.
Common mistakes
Do not treat the HP cost as harmless just because it stops below 1% HP. Danjin can still take damage from enemies, and the Dodge Counter version of Crimson Erosion (Skill) doubles its usual HP cost. Watch her health before committing to another sequence of attacks.
Do not switch to your Havoc teammate too early after applying Incinerating Will. The mark increases Danjin's damage against that target, while Duality is the separate boost for the incoming character. Also avoid switching that character out before you have used the Outro effect.
Do not assume the description's higher Ruby Blossom multiplier has a clear threshold. It says the increased multiplier applies above 120 Ruby Blossom, while also stating that Danjin can hold up to 120. The description does establish that Chaoscleave (Forte) is available from 60.