Siris - Ksana

If you don't have Siris - Ksana yet but want to try her out, she is available as a Trial Operative in Story Chapter SP2 "Realm of Illusion" (Legacy // New Hentiro // Realm of Illusion)

Ksana charges at enemies, allowing her great mobility, and with decent damage.
Whilst her dps is still ok, Powercreep means that Ksana isn't a great dps any more, and her constant movement can be annoying, and a major weakness against specific enemies.
Ksana's good mobility and bulk can also give her decent survivability, but constantly charging into melee range of enemies can give her very poor surviability too.

The Basics

Role: Main DPS
Deals Thermal Damage
Weapon Type: Shotgun
Deals entirely skill damage
Mobility is amazing

How to use Siris - Ksana

Use Siris' Standard Skill to create a shield and rush forward. Ram into enemies and push them
When her Standard Skill is charged, use it again to shatter Ksana's shield.
This deals a lot of damage in a small AoE in front of her.
When Siris has at least 100 Resilience, use her ult if available.
(120 Resilience if Ksana has her Manifestation.1 buff.)
(Resilience is the gauge in the centre of the screen.)

Repeat

(Note: Siris never shoots her gun.)

How to build Siris - Ksana

Weapon: Crowned Flail / Scarabaei
Weapon Parts: Max HP or ATK
Whichever is higher: 8x ATK or 1x Max HP
Logistics Squad: Scarab
+10.0% HP
+10.0% ATK
+8.5% Thermal Damage
Best teammates:
Vidya - Celestial Swan
Siris - Freefin
Marian - Aquila

Specifics

Standard Skill

Siris creates a shield in front of her, and charges forwards.
The shield deals Thermal damage and knocks back enemies, allowing Siris to push enemies around.
The shield also grants Siris damage reduction from frontal attacks, and gives her CC-resistance.
Siris can dodge to stop her charge and remove the shield.

If Siris has any S-Energy, then she'll use 5 each second to give herself even more damage reduction, as well as gain 2 "Resilience" - which is used for her ult.
She also gains 1 Resilience when the shield hits an enemy.
Siris' Deiwos also gives her 1 stack of "Rejuvenation" for every 20 Resilience she gains or loses. Each Rejuvenation gives Siris +2% ATK.
Each +100 Alignment Index gives each Rejuvenation stack +0.5%.
This stacks up to 20 times, and Siris loses 1 stack every 5s.
Since most of Siris' damage comes from her Max HP stat, not her ATK, this isn't the biggest damage buff ever, and isn't as large as it would be on other dps operatives.

The shield is enhanced after a short period.

Using Siris' Standard Skill again shatters the shield to deal AoE thermal damage in front of her. Shattering also grants some U-Energy.
The damage is higher if the shield was enhanced.

This skill has a 4s cooldown, which starts after Siris stops sprinting.
If the shield was enhanced, then it hitting a target when it shatters restores S-Energy, and also lowers its cooldown if Siris has a Thermal weapon.

The shields contact damage is entirely determined by Siris' Max HP.
The shatter damage is determined by both Siris' ATK and her Max HP. Most of this shatter damage comes from her HP, not from her ATK.

Ultimate Skill

Siris freezes time, and charges an attack that deals damage to 5 enemies in front of her.
If there are at least 5 enemies, then 5 different enemies are chosen.
If there are less than 5 enemies available, the same enemy is hit multiple times, but takes less damage for each subsequent hit.
Siris uses Resilience to charge this attack, which increases its damage, using up to 100 Resilience, gaining +0.9% Final damage per Resilience.
(So using the full 100 Resilience gives +90% Final damage.)
She can still use her ult even if she doesn't have 100 Resilience - she just won't max the damage bonus it gives.

With its first Neuronic buff, the cooldown of her ult is reduced by 0.3s whenever Siris deals any non-ultimate damage.
With lots of enemies to charge into, this allows Siris quite a short cooldown.

Note that Siris' ult has an extremely low U-Energy cost of 15, allowing her to use it very frequently.
Ksana is often just limited by her Resilience generation.

Her ults damage is determined by both Siris' Max HP and her ATK.

Support Skill

Siris deals PBAoE Thermal damage, and gives all allies a shield that absorbs damage for 10s.
Both the damage and the damage absorption are based on Siris' Max HP, not her ATK.

Like all main dps operatives, Siris doesn't work well as a support.

Weapon

Crowned Flail
Her 5* weapon, and her best weapon.
This increases Siris' Max HP and ATK, as well as giving her Thermal damage.
Crowned Flail's Thermal damage buff lasts 0.5s and is granted by using her Standard Skill.
As such, with Crowned Flail, Siris will want to use her ult immediately after using her Standard Skill.
Scarabaei
Her 4* event weapon.
Max HP and Thermal damage, which is good, with more Thermal damage based on Max HP.

Siris really wants a Thermal damage shotgun to proc her Neuronic buff, so if you don't have Crowned Flail or Scarabaei, then just use whatever Thermal-damage shotgun you have.

For weapon Parts Siris wants Max HP or ATK
Siris' skills deal damage based on Max HP and ATK - her ATK multipliers are 8x the Max HP multipliers.
As such, which is better depends on which is higher.
If an ATK buff is 8x higher than the Max HP buff, then the ATK buff is better.
If the ATK buff isn't 8x higher than the Max HP buff, then the Max HP buff is better.

Logistics

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

Scarab basically just gives Ksana more ATK and Max HP (and thus more damage) and more Thermal damage.

For stats:
Basic Stats: +10.0% Max HP and +10.0% ATK.
Special Stats: +8.5% Thermal DMG.

Very simple.

Siris' damage is based on both her Max HP and her ATK, so she wants both of those stats.
Siris also deals entirely Thermal damage, so Thermal damage for her special stat.

Cope stats include:

Alignment Index Three maxed Alignment Index rolls will give +1.59% ATK per Rejuvenation stack (so +31.8% ATK when maxed).
Siris' M1 and M2 help Siris get more Resilience/Rejuvenation, so Alignment Index is more useful if Siris has those.
Siris is still better off with the damage from Max HP and ATK though.
S-Energy Recovery Since Siris can still use her standard skill even with no S-Energy, Siris is better off with the extra damage from Max HP and ATK.
More S-Energy regen will help sustain her S-Energy buffs, but even three maxed S-Energy regen rolls doesn't help much against a drain of 5 S-Energy/s
Just go for more damage instead.
For almost all content, Siris' second Neuronic that gives S-Energy after shattering is all you need.

Manifestations

M1 just gives Siris +2 Resilience per second, and increases the amount her ult can use to 120.
Going from 100 to 120 means her ult goes from 190% final damage to 208%, which is effectively a 9.5% increase.
M1 allows Siris to cycle her ult faster and with more damage, increasing her dps.
M2 gives Siris 4 stacks of Rejuvenation whenever she consumes the max of 120 Resilience.
With M2 you'll want to always use Siris' ult at max Resilience stacks, but you were probably doing that anyway.
The extra Rejuvenation is a nice damage bonus though should you not already be maxing it.
If you could already max Siris' Rejuvenation stacks, then M2 doesn't help her sustained damage at all.
It does help her to get to the max sooner though, so even if you could max it without M2, M2 can still be useful.
M3 gives Siris +20% Thermal DMG if she has 5+ stacks of Rejuvenation.
Given her M1 and M2 bonuses, this isn't hard to maintain.
This isn't a Final damage bonus though, so it's not too strong.
M4 gives the usual +1 ultimate skill level, increasing its damage.
This is a nice damage bonus, but doesn't change how Siris is played at all.
With M5, Siris using her ult increases the Final DMG her Resilience gives from 0.9% to 1%.
A nice damage bonus for sure, but it's just more damage.

Siris' M1 is a nice QoL buff, and if you want to play Siris at all you should get her M1 buff.
Her M2-M5 buffs are just more damage.

For casual content, M1 is a good stopping point - M2 doesn't help much with casual content, and M3 isn't that strong.
For endgame content, M3 is an efficient stopping point should you not want to invest all the way to M5.

Good Supports for Siris - Ksana

Ksana deals entirely skill damage, so any support that buffs skill damage will be good for her.
Siris also deals Thermal damage, so Thermal-damage buffs are also useful to her.

Unlike most main dps operatives though, Siris' damage is largely based on her Max HP, and only partially based on her ATK.
ATK buffs are thus less useful for Siris than for other dps operatives.
This makes support operatives who can only buff ATK (e.g. Eatchel - The Cub) much less useful for Ksana than for other dps operatives.

Ksana has very high HP and naturally gains some damage reduction effects, and thus Ksana can have very good survivability, although somewhat reduced due to her proximity to enemies.
This means Ksana does not necessarily need healing as much as other operatives.
Sometimes she needs more though - it depends on what you're fighting.

Support operative that work well with Siris - Ksana:

Vidya - Celestial Swan
Celestial Swan reduces the enemies DEF and Resistance, massively increasing the damage they take.
If using Celestial Swan, make sure the other support either doesn't deal damage or deals the same type of damage as Ksana. (I.e. isn't off-element).
Siris - Freefin
Ksana deals skill damage very rapidly, allowing her to easily gain Siris' Wavehunt, and trivially maintain Freetide, and Siris provides lots of skill damage buffs to Ksana.
Freefin's +ATK boosts are less useful for Ksana though, but she's still a great support for Ksana.
Marian - Aquila
Aquila provides very strong generic damage buffs, which makes her an excellent support.
Aquila is off-element to Ksana (Aquila constantly deals Kinetic damage).
Marian - Riptide
Riptide provides some nice skill damage buffs to Ksana.
Note that Riptide is off-element to Ksana (Riptide deals Chaos damage)
Acacia - Kaguya
If you can't use Celestial Swan, then Kaguya performs a similar role.
Kaguya is much weaker than Celestial Swan though.

A lot of the usual cope Supports like Agave and [Redacted] etc. don't work well with Ksana because Ksana gains less benefit from ATK buffs than other operatives.
Chenxing - The Observer's skill buffs are useful, but Siris' mobility and ability to push enemies can make it difficult to stay in Chenxing's AoE.
This makes Chenxing very difficult to use with Ksana.

Tess - The Magician is generally wasted on Ksana, as Ksana's ult requires only 15 U-Energy, and mostly wants Resilience stacks, which Tess doesn't help with.
As such Tess doesn't really help Ksana that much.
Tess' damage buffs are still useful, but overall Tess isn't a great support as her damage buffs are weak in comparison to actual skill damage supports like Freefin.

Since Ksana never actually shoots anything, she'll never charge the Zephyr Machine from Enya - Exuvia's support skill, and hence it will never deal damage.
Enya's skill damage buffs are still ok, but overall Exuvia isn't a great support for Ksana.

Not shooting anything also means that per-shot aptitude buffs like Tess - Phantasia and Fritia - Little Sunshine are wasted on Ksana.