Katya - Dawnwing

Katya - Dawnwing is not currently available as a Trial Operative, so if you want to try her out then you'll have to wait until her banner next comes around.

Dawnwing has fantastic mobility, a pretty simple rotation, doesn't need to reload, can go through most enemy barriers, is good against both trtash mobs and single-targets, and is very consistent, but does constantly move around and requires a decent amount of skill spamming.
Dawnwing is a very strong all-round operative - great damage, great mobility (and thus great survivability), but to get the best out of her requires maximum investment.

Overall

Role: Main DPS
Deals Frost Damage
Weapon Type: Assault Rifle
Deals mostly skill damage
but does deal ok ballistic damage
Mobility is fantastic

How to use Katya - Dawnwing

Hold your Standard Skill to create Crystal Vanes until you have at least 6 of them.
Shoot an enemy until her passive procs, with the Vanes dealing dmg
3 Crystal Vanes will also be removed
If Dawnwing has 6 Crystal Vanes, use her Ult off-cooldown.
(Ideally use her ult right after her Vanes proc in Step.2)

Repeat

Notes:

Use her standard skill to stack Vanes during boss invuln phases
Shoot bosses to nearly-max the gauge during their invuln phases
(So her next shot procs her Vanes)
If you haven't turned off Ultimate Animations in the options, then her ult isn't always worth using in multiplayer content.

How to build Katya - Dawnwing

Weapon: Aurora Sands / Tornado
Weapon Parts: Max ATK
Logistics Squad: Vector
+10.0% ATK
+106 Alignment Index
+8.5% Frost Damage
Best supports:
Vidya - Celestial Swan
Tess - Phantasia
Siris - Freefin

Standard Skill

Tapping Dawnwing's Standard Skill causes her to dash in the direction she is moving in (or forward if she isn't moving) and create 1 Crystal Vane.
If you hold the skill down it will cause Katya to do two dashes, and create 3 Crystal Vanes. (whilst still using the same S-Energy as a single dash)
The two dashes don't have to be in the same direction - you can dash one way, then dash the opposite way, and end up back where you started.
This is recommended and doesn't require much practice to do.
Further note that the dash (as well as Dawnwing's regular dodge) is more of a phase, and does allow her to go through almost all enemy-created barriers.
Dawnwing uses her skill a lot, and that it moves her a lot gives Dawnwing a lot of mobility.

Dawnwing can have a max of 12 Crystal Vanes at once.

Dawnwing's Standard Skill does also deal some PBAoE Frost damage when creating a Crystal Vane.
This isn't much damage, but it's something, and is good enough for clearing trash mobs.
Against bosses, staying near the boss so this PBAoE damage hits them will increase your damage a little, but that's generally not necessary.

You may wish to get Dawnwing to 12 Crystal Vanes before using a debuff (e.g. Vidya - Celestial Swan), so that you don't need to create Crystal Vanes during the debuff and can just do damage, in order to make the best use of the debuff as you can.

Note that a few in-game effects treat the two parts of Dawnwing's Standard Skill dash as separate skills/effects
For example the effect "50% of S-Energy consumed when using a skill is converted into U-Energy" buff gives U-Energy for both the first and second dash
(Granting 4 and 3 U-Energy respectively) [If you only do one dash you only get the first lot of 4 U-Energy]

Passive Effect

Dawnwing has a gauge near the middle of the screen that fills.

This gauge fills slowly when in combat, or quickly when shooting.
(Max is 100. Gain 10/s naturally, as well as 4 per shot hit.)
When full, the next shot Dawnwing fires will reset the gauge and trigger her Crystal Vanes - Up to 6 Crystal Vanes will fire at the shot enemy, dealing high Frost damage.
After proc'ing the passive, some Crystal Vanes disappear (how many disappear depend on how many you have. With 6 or more Vanes up, 3 Vanes will disappear)

The damage from her Vanes proc'ing and firing at enemies is where most of Dawnwing's damage comes from.

Since a maximum of 6 vanes proc, having more than 6 vanes up doesn't increase the damage of Dawnwing proc.
You can use periods of downtime (e.g. enemy invulnerability phases) to build vanes, so that you don't need to make them during combat and can focus on just on proc'ing the crystals rather than making them, which helps Dawnwing's dps a little.

For each Crystal Vane that fires at an enemy, Dawnwing recovers 4 bullets.
With the max of 6 Crystal Vanes firing, this means Dawnwing recovers 4*6=24 bullets per proc.
Due to Dawnwings natural aurora regeneration (10/s) means it actually takes her a little less than 24 bullets to proc her vanes, which recover 24 bullets.
This means that [provided you land your shots] Dawnwing never needs to manually reload.

Shooting an enemy builds the gauge, even if the enemy is invulnerable.
This allows you to build the gauge to full whilst an enemy is invulnerable so that when they become vulnerable again your next shot proc's Dawnwing's Crystal Vanes.

Note that in practice you don't need to worry about her Crystal Vanes - just use her standard skill to dash twice after the vanes fire, and you'll always stay at or above 6.

Dawnwing will also use her standard skill automatically when switched in (This doesn't use any S-Energy or skill charges though)
This does create Crystal Vanes, but since it's her standard skill it does also cause her to move, which can make it a liability in certain situations.
Especially if you only move once and don't dash twice to end up back where you started.
Note that for Dawnwing to double-dash when switched in you need to hold her standard skill key (Default: E) down, not her swap-in key.
This does require some practice.

Ultimate Skill

Dawnwing's Ultimate Skill causes her to shoot a huge arrow at the target that deals Frost damage.
This also causes Dawnwing to use up to 6 Crystal Vanes (if you have them) to fire a ray at the target, causing up to 3 Vanes to dissapear, as usual.
(The game says "up to 6 Crystal Vane(s) will dissappear" but that's wrong - just like her regular proc it's 3 max.)
...this does mean that Dawnwing's Ultimate skill is just her Vane proc with an extra Frost Damage projectile on top.

Dawnwing's Ultimate Skill also restores all her standard skill charges, allowing you to immediately use your Standard Skill again.
Against bosses (and with mostly perfect play) this isn't actually needed, but it is useful if you miss some shots and/or are running out of S-Energy due to using your Standard Skill to clear trash mobs.

In Single-Player content, time massively slows down when you use your Ultimate.

In Multi-player content time does not slow down, but you can disable the animations for Ultimate Skills in the options menu, making them activate much faster.
If you haven't disabled the animations, then Dawnwing's long ult animation and her high non-ult dps means that her ult isn't really worth using - it just takes too long for its damage.
If you want to main Dawnwing, or use her in multiplayer content a lot, then I strongly recommend that you disable ultimate animations

Weapon

Aurora Sands
Her 5* weapon, and her best weapon.
Aurora Sands givs her more ATK, more Skill Damage, and increases the damage enemies take from Dawnwing's Standard Skill, which is very strong.
Tornado
Her 4* event weapon. A bit more clunky in its buffs, but still good.

If you don't have either of those, you are generally best off using the 3* Icey Dunes, especially if you want/need a Frost-damage weapon.
If you don't need a Frost-damage weapon, then you can use whatever you have lying around just fine, although good choices include Wild Leer and Ashen Fortress (if you have it).

For weapon Parts Dawnwing wants max ATK.

Logistics

Use Vector squad - it was designed specifically for her and is her best choice.

Vector gives Dawnwing a huge damage buff for her Crystal Vanes, which are what deal most of her damage.
It also gives a 5% ATK buff her Vane hit, up to 4 stacks.
Maxing this buff is absolutely trivial.

For stats Dawnwing wants:
+10.0% ATK
+106 Alignment Index.
For the Special talent, Dawnwing want 8.5% Frost Damage

ATK for more damage.

Alignment gives her more ATK per Vane on the field, up to 6, which you should always have, making the buff essentially permanent.
All 3 Logistics officers having max Alignment Index rolls gives Dawnwing +19.08% ATK.

Most of Dawnwing's damage comes from her Crystal Vanes, which is skill damage, and skill damage can't crit, so crit mods are not very strong for her as they'd only affect her ballistic damage, which is a minority of her overall damage.
Dawnwing's ult isn't a massive dps boost, so U-Energy Regen isn't very good
Dawnwing has no S-Energy issues, so S-Energy Regen isn't useful
Dawnwing doesn't heal or create shields, so increases to those stats are useless for her

Whilst Dawnwin does have some cope stats, no stats other than ATK, ALignment, and Frost DMG actually provide her with any major benefit.

Manifestation

M1 causes Dawnwing's Vanes to ignore 25% of the enemies DEF whilst Dawnwing has a Frost-damage weapon equipped (i.e. hopefully always)
This is quite a nice damage boost.
M2 causes her Crystal Vanes to fire a second shot that deals 15% the damage of the original (but doesn't proc her other effects, like giving her bullets)
Since most of Dawnwings damage comes from her Crystal Vanes, this does add a lot of damage to her.
M3 causes her Crystal Vanes' damage to ignore 12% of the enemies Resistance, which is a very nice damaage buff.
M3 also causes Dawnwing to use her Standard Skill for free whenever she is swapped in.
Since this includes any swap in, this also works when Dawnwing swaps in after using the ult of a support operative (or sometimes support skill)
For some support operatives that you want to use at the start of a fight (e.g. Vidya - Celestial Swan), you can use their ults, and use the freeStandard Skill use her M3 gives her to get Dawnwing a lot of Vanes very quickly. This can be tedious to do, but does allow Dawnwing to get her Vanes up much faster than she otherwise would.
M4 is the standard +1 skill level to her Standard Skill, resulting in around +10% damage.
M5 increases Katya's Final Skill DMG by 2% per Vane she has, up to 6 stacks.
Since most of Katya's damage comes from her Vanes, +12% Final Skill DMG is very strong.

All of Dawnwing's Manifestations increase her damage by a good amount.
This means that you ideally want Dawnwing to be at M5 for max damage.

If you don't want to invest that much into Dawnwing, you can stop at any point, but not getting to M5 will give Dawnwing notably reduced damage when compared to her at M5.

This is also why Dawnwing wants high investment - each of her Manifestations add a lot to her damage, and she ideally wants all of them.
Similarly, Dawnwing's T5 weapon is also a large increase to her damage.

Good Supports for Katya - Dawnwing

Most of Dawnwing's damage comes from her Crystal Vane procs (which is skill damage), not from her shooting, meaning that ballistic buffs are not overly useful for Dawnwing.
Instead, Dawnwing wants skill damage buffs or debuffs to enemies damage resistances.
Despite this, Dawnwing does shoot a lot and ideally never needs to reload, and thus per-shot buffs are still very useful to her as she spends most of her time in combat shooting.

Vidya - Celestial Swan (and other resistance shredders)
Celestial Swan and other resistance shredders (Acacia - Kaguya, etc.) that reduce the enemies resistance help enemies take more damage.
If using Celestial Swan, make sure the other support isn't off element to Dawnwing.
Tess - Phantasia
Per-shot Frost damage works out very well for Dawnwing, due to Dawnwing spending most of her time in combat shooting stuff with a high-RoF AR.
Phantasia is also on-element to Dawnwing, allowing her to be used alongside Celestial Swan.
Siris - Freefin
Freefin provides strong skill damage buffs, although Dawnwing can't make use of Freefin's Wavehunt thermal damage buff, and Siris doesn't buff Dawnwing's ballistic dmg.
Freefin's support skill deals Thermal damage, but Dawnwing can generally maintain Siris' buffs just fine, and hence Siris can maintain her buffs.
Being able to maintain her buffs and thus not need to re-cast her support skill means that Dawnwing and Freefin can work with Celestial Swan.
Marian - Riptide
Dawnwing's damage rotation is short, so it's easy for Riptide to swap in and maintain her buffs, which makes her skill damage buffs good for Dawnwing.
Note that Riptide is off element to Dawnwing (Riptide deals Chaos damage)
Enya - Exuvia
Continually shooting whilst wanting mostly skill damage buffs for her constant skill usage makes Exuvia a good support for Dawnwing.
Exuvia is off-element to Dawnwing though (Exuvia deals Electric-damage)
Eatchel - The Cub
Dawnwing's extreme mobility means she doesn't massively need Eatchel's healing buffs, but Eatchel's ATK buffs are still good.

Note that Tess - The Magician doesn't really work very well with Dawnwing, as Dawnwing's Ult is basically a slightly stronger version of her Standard Skill, and isn't a large enough dps increase to justify using an entire support operative to use her ult faster, especially as the requirement to create Vanes first means you can't use her ult instantly anyway.

Similarly, Dawnwing's ballistic dps is a small percent of her damage, with most of her damage being from her Crystal Vane proc.
This means that ballistic supports like Yao - Nightglow aren't overly useful to her.
Similarly, again, since she never needs to reload, buffs to magazine capacity or reloading buffs (i.e. Fenny - Starshine) aren't useful either.