Bronya is a Wind Element Character that follows the Path of Harmony. Her kit revolves around her sequencing her Skill, Basic ATK, and ULT.
Her skill allows a single target ally to advance forward in an instant, boost the DMG and negate a debuff. Meanwhile, her ULT enhances the entire team's ATK and Crit DMG.
She is a well rounded support for a team with Main DPS that focuses on ATK Stat, yet her skill can be a burden as it is SP Unfriendly.
Best Cavern Relics
(2) Increases SPD by 6%.
(4) When using Skill or Ultimate on one ally target, increases the ability target's CRIT DMG by 18%, lasting for 2 turn(s). This effect can stack up to 2 time(s).
This set is considered as her best so far despite the fact that the wearer must only target a single ally. Bronya's ULT affects the entire team which makes it harder for her to quickly max up the Crit DMG buff.
(2) Increases SPD by 6%.
(4) When the wearer uses their Ultimate on an ally, SPD for all allies increases by 12% for 1 turn(s). This effect cannot be stacked.
This set's all ally SPD buff is good for Bronya since it doesn't require a single target for it to take effect.
(2) Increases Wind DMG by 10%.
(4) After the wearer uses their Ultimate, their action is Advanced Forward by 25%.
This set is mainly for Main DPS, but it also allows support characters to take turns faster after initiating their ULT.
Best Planar Ornaments
(2) Increases the wearer's Effect RES by 10%. When the wearer's Effect RES is at 30% or higher, all allies' CRIT DMG increases by 10%.
The Crit DMG from Bronya's ULT may be good, but having this set with her is also great for the entire party.
(2) Increases the wearer's Energy Regeneration Rate by 5%. If the wearer is not the first character in the team lineup, then increases the ATK of the first character in the team lineup by 12%.
This helps Bronya with her energy and ULT uptime as well as buffing the 1st character of the team.
(2) Increases the wearer's Max HP by 12%. When the wearer's SPD reaches 120 or higher, all allies' ATK increases by 8%.
Overall, this set allows Bronya to instantly enhance the entire team's ATK, she only requires 120 SPD - which is easy to obtain with SPD boots.
Best Stats

Body
CRIT DMG

Boots
SPD

Sphere
HP% / DEF%

Rope
Energy Regeneration Rate
Substats
CRIT DMG / SPD / HP% / DEF% / Effect RES
info
The only thing that Bronya requires is having 150% or greater Crit DMG and at least 150% SPD to give her fast turns. Her Basic Attack will gain 100% Crit Rate after using her Skill, so she doesn't need much Crit Rate Stats.
Do mind that she is an SP Unfriendly Character unless her turn cycle is followed (Skill> BA > Skill> BA > ULT).
Best Light Cones
SourceLight Cone Event Warps
Departing Anew
After the wearer uses Skill or Ultimate on one ally character, the wearer regenerates 6.0~8.0 Energy and the ability's target receives 1 stack of "Hymn" for 3 turn(s), stacking up to 3 time(s). Each stack of "Hymn" increases its holder's DMG dealt by 15~24%. After every 2 instance(s) of Skill or Ultimate the wearer uses on one ally character, recovers 1 Skill Point.This Lightcone's overall mechanics focuses more on single ally target, yet offers better for Bronya.
SourceStellar Warp, Light Cone Event Warp, Starlight Exchange, Stellar Convergence
Heir
Increases the wearer's Energy Regeneration Rate by 10~18% and regenerates 1 Skill Point when the wearer uses their Ultimate on an ally. This effect can be triggered once after every 2 uses of the wearer's Ultimate. When the wearer uses their Skill, the next ally taking action (except the wearer) deals 30~50% more DMG for 1 turn(s).This grants Bronya with ER she needs for her ULT uptime as well as regenerating 1 Skill Point, however, the latter effect can only be triggered after 2 usage of her ULT. An ally will enjoy high DMG buff whenever they take turns after Bronya.
SourceLight Cone Event Warp
Capriciousness
Increases the wearer's CRIT DMG by 32~60%. At the start of the battle, the wearer gains Mask, lasting for 3 turn(s). While the wearer has Mask, the wearer's allies have their CRIT Rate increased by 10~14% and their CRIT DMG increased by 28~56%. For every 1 Skill Point the wearer recovers (including Skill Points that exceed the limit), they gain 1 stack of Radiant Flame. And when the wearer has 4 stacks of Radiant Flame, all the stacks are removed, and they gain Mask, lasting for 4 turn(s).This LC focuses more on buffing Bronya's Crit Stats rather than offering buffs to her allies. However, it allows her to enhance her ally target with better stat increase.
SourceJeweler's Pagoda, Echo of War, Memo-Keeping Light Casket, Light Cone Manifest
Kites From the Past
When the wearer uses their Skill, the next ally taking action (except the wearer) deals 16~32% increased DMG for 1 turn(s).Through her Skill, Bronya adds up more DMG boost to her target ally. It is easily triggered since she advances them forward instantly.
SourceStellar Warp, Departure Warp, Character Event Warp, Light Cone Event Warp
Cannot Stop It!
When the wearer uses their Ultimate, all allies' actions are Advanced Forward by 16~24%.This allows the wearer to advance forward the whole team by up to 24%, giving them a chance to steal turns and prevent disastrous failure.
Secret
At the start of the battle and whenever the wearer's turn begins, one of the following effects is applied randomly: All allies' ATK increases by 10~20%, all allies' CRIT DMG increases by 12~24%, or all allies' Energy Regeneration Rate increases by 6~12%. The applied effect cannot be identical to the last effect applied, and will replace the previous effect. The applied effect will be removed when the wearer has been knocked down. Effects of the same type cannot be stacked.
This randomly provide ATK, CRIT DMG, or ER buff. However, due to its RNG mechanic, it doesn't offer that much support especially on hardcore contentes