Honkai: Star Rail Firefly Character Guide

Firefly is a damage dealer who fights using her mech armor, SAM. By activating her Ultimate, she enters the COmplete Combustion state, enhancing her abilities.
In this state, SAM has increased Break capabilities and Break DMG, and she can also deal partial Toughness Reduction to enemies that are not weak to Fire. Additionally, she can apply Fire Weakness to enemies using her Technique or Enhanced Skill.

Skills Overview

Basic Attack - Order: Flare Propulsion

Deals Fire DMG equal to 50%—110% of SAM's ATK to a single target enemy.

Skill - Order: Aerial Bombardment

Consumes SAM's HP equal to 40% of SAM's Max HP and regenerates a fixed amount of Energy equal to 50%—62% of SAM's Max Energy. Deals Fire DMG equal to 100%—220% of SAM's ATK to a single target enemy. If the current HP is not sufficient, then SAM's HP is reduced to 1 when using this Skill. Enables this unit's next Action to be Advanced by 25%.

Enhanced Basic Attack - Fyrefly Type-IV: Pyrogenic Decimation

Restores HP by an amount equal to 20% of this unit's Max HP. Deals Fire DMG equal to 100%—220% of SAM's ATK to a single target enemy.

Enhanced Skill - Fyrefly Type-IV: Deathstar Overload

Restores HP by an amount equal to 25% of this unit's Max HP. Applies Fire Weakness to a single target enemy, lasting for 2 turn(s). Deals Fire DMG equal to (0.2 × Break Effect + 100%—220%) of SAM's ATK to this target. At the same time, deals Fire DMG equal to (0.1 × Break Effect + 50%—110%) of SAM's ATK to adjacent targets. The Break Effect taken into the calculation is capped at 360%.

Ultimate - Fyrefly Type-IV: Complete Combustion

Upon entering the Complete Combustion state, Advances SAM's Action by 100% and gains Enhanced Basic ATK and Enhanced Skill.
While in Complete Combustion, increases SPD by 30—66, and when using the Enhanced Basic ATK or Enhanced Skill, increases this unit's Weakness Break efficiency by 50% and the Break DMG received by the enemy targets by 10%—22%, lasting until the current attack ends.

A countdown timer for the Complete Combustion state appears on the Action Order. When the countdown turn starts, SAM exits the Complete Combustion state. The countdown has a fixed SPD of 70. SAM cannot use Ultimate while in Complete Combustion.

Talent - Chrysalid Pyronexus

The lower the HP, the less DMG received. When HP is 20% or lower, the DMG Reduction reaches its maximum effect, reducing up to 20%—44%. During the Complete Combustion, the DMG Reduction remains at its maximum effect, and the Effect RES increases by 10%—34%.
If Energy is lower than 50% when the battle starts, regenerates Energy to 50%. Once Energy is regenerated to its maximum, dispels all debuffs on this unit.

Technique - Δ Order: Meteoric Incineration

Leaps into the air and moves about freely for 5 seconds, which can be ended early by launching a plunging attack. When the duration ends, plunges and immediately attacks all enemies within a set area. At the start of each wave, applies a Fire Weakness to all enemies, lasting for 2 turn(s). Then, deals Fire DMG equal to 200% of SAM's ATK to all enemies.

Ascension 2 - Module α: Antilag Outburst

During the Complete Combustion, attacking enemies that have no Fire Weakness can also reduce their Toughness, with the effect being equivalent to 55% of the original Toughness Reduction from abilities.

Ascension 4 - Module β: Autoreactive Armor

When SAM is in Complete Combustion with a Break Effect that is equal to or greater than 200%/360%, attacking a Weakness-Broken enemy target will convert the Toughness Reduction of this attack into 1 instance of 35%/50% Super Break DMG.

Ascension 6 - Module γ: Core Overload

For every 10 of SAM's ATK that exceeds 1800, increases SAM's Break Effect by 0.8%.

TLDR

Ignore her Basic ATK because you should never use it in the battle (unless you want the Skill Points). What you need to focus on is her Skill, Ultimate, and her Enhanced Skill.

First of all, her Skill is not that big of a deal except for the Energy Regeneration. That extra Energy is a godsend because you need to get her Ultimate as soon as possible because that's her main source of damage.

Now for her Ultimate, it does a LOT of things.
(1) The most important one is it will let Firefly enter the Complete Combustion state.
(2) Then, advance her turn by 100%, which means she will have her turn again immediately after using Ultimate.
(3) Increase her SPD, increase her Weakness Break efficiency, and increase her Break DMG.

Once she enters her Complete Combustion state, this is where Firefly truly shines. It will let her use Enhanced Basic ATK and Enhanced Skill. Ignore the Enhanced Basic ATK (unless you want the Skill Points) and make sure you always use her Enhanced Skill. The Enhanced Skill will apply Fire Weakness to a single target enemy, deal a truckload of damage, and also heal Firefly. It's the full combo set and should not be missed in every turn.

Traces Priorities

Ultimate = Skill > Talent > Basic ATK

Recommended Light Cones

1. Whereabouts Should Dreams Rest (5⭐)
2. On the Fall of an Aeon (5⭐)
3. Indelible Promise (4⭐)

1) Whereabouts Should Dreams Rest

Increases the wearer's Break Effect by 60~100%. When the wearer deals Break DMG to an enemy target, inflicts Routed on the enemy, lasting for 2 turns. Targets afflicted with Routed receive 24~40% increased Break DMG from the wearer, and their SPD is lowered by 20%. Effects of the similar type cannot be stacked.

2) On the Fall of an Aeon

Whenever the wearer attacks, their ATK is increased by 8~16% in this battle. This effect can stack up to 4 time(s). After a character inflicts Weakness Break on an enemy, the wearer's DMG increases by 12~24% for 2 turn(s).

3) Indelible Promise

Increases the wearer’s Break Effect by 28~56%. When the wearer uses their Ultimate, increases their CRIT Rate by 15~30%, lasting for 2 turn(s).

Recommended Relics & Planar Set

1. Relics
   • Iron Cavalry Against the Scourge
   • Thief of Shooting Meteor
2. Planar Set
   • Forge of the Kalpagni Lantern
   • Talia: Kingdom of Banditry

Cavern Relics

Relic Set (Iron Cavalry Against the Scourge)

2-Piece: Increases Break Effect by 16%.
4-Piece: If the wearer's Break Effect is 150% or higher, the Break DMG dealt to the enemy target ignores 10% of their DEF. If the wearer's Break Effect is 250% or higher, the Super Break DMG dealt to the enemy target additionally ignores 15% of their DEF.

Relic Set (Thief of Shooting Meteor)

2-Piece: Increases Break Effect by 16%.
4-Piece: Increases the wearer's Break Effect by 16%. After the wearer inflicts Weakness Break on an enemy, regenerates 3 Energy.

Planar Ornaments

Planetary Set (Forge of the Kalpagni Lantern)

2 Piece: Increases the wearer's SPD by 6%. When the wearer hits an enemy target that has Fire Weakness, the wearer's Break Effect increases by 40%, lasting for 1 turn(s).

Planetary Set (Talia: Kingdom of Banditry)

2 Piece: Increases the wearer's Break Effect by 16%. When the wearer's SPD reaches 145 or higher, the wearer's Break Effect increases by an extra 20%.

Main & Sub Stats Priority

Team Recommendations

Ultimate Firefly Team

This is definitely the best team for Firefly because each of them can help SAM with Break Effect buffs. Ruan Mei is a core character in the team, so if you didn't have her, it would lead to a pretty big DPS loss for Firefly.
Firefly: Main DPS
Harmony Trailblazer: Core Support for Super Break DMG (Irreplaceable)
Ruan Mei: Support for Break Effect (Irreplaceable-ish) || If you don't have Ruan Mei, you can replace her with Asta or Pela, although they will never reach Ruan Mei's position in this team)
Gallagher: Flex (He also contributes, and inflicts Break debuff on enemies) || Can be replaced with any other support, either healer/shielder or another Harmony/Nihility. He's the best in the Firefly team because he's a sustainer that scales with Break Effect.

Eidolons

Best Eidolons: E1, E2 & E6

E1: In Reddened Chrysalis, I Once Rest ⭐
When using the Enhanced Skill, ignores 15% of the target's DEF. And the Enhanced Skill does not consume Skill Points.

E2: From Shattered Sky, I Free Fall ⭐
When using the Enhanced Basic ATK or the Enhanced Skill in Complete Combustion state to defeat an enemy target or cause them to be Weakness Broken, SAM immediately gains 1 extra turn. This effect can trigger again after 1 turn(s).

E3: Amidst Silenced Stars, I Deep Sleep
Skill Lv. +2, up to a maximum of Lv. 15.
Basic ATK Lv. +1, up to a maximum of Lv. 10.

E4: Upon Lighted Fyrefly, I Soon Gaze
While in Complete Combustion, increases SAM's Effect RES by 50%.

E5: From Undreamt Night, I Thence Shine
Ultimate Lv. +2, up to a maximum of Lv. 15.
Talent Lv. +2, up to a maximum of Lv. 15.

E6: In Finalized Morrow, I Full Bloom ⭐
While in Complete Combustion, increases SAM's Fire RES PEN by 20%. When using the Enhanced Basic ATK or Enhanced Skill, increases the Weakness Break efficiency by 50%.