Winter Altina

Weapon: Ragnell•Alondite (+Eff)

Assist: Ardent Sacrifice / Positional Assist 

Special: Twin Blades / Aether

Passive A: Atk/Res Finish / Atk/Res Unity / Mirror Stance 3 / Atk/Def versions of mentioned skills

Passive B: Atk/Def Bulwark / Mystic Boost 4 / Quick Riposte 4 / Special Spiral 4 / Null C-Disrupt

Passive C: Atk/Res Oath 4 / Joint Drive Atk / Pulse Smoke / Atk Smoke 4

Sacred Seal: Atk/Res Ideal / Atk/Res Form / Mystic Boost / Atk/Def or Def/Res versions of mentioned skills

• This is a more traditional, secure take on Aether Raids tanking if the threat of Duo's Hinderance is too risky or the higher-risk high-reward Vantage playstyle isn't your groove. Thanks to Ragnell•Alondite's cooldown acceleration and Brave effect, Altina/Sanaki gains the distinctive advantage of being able to activate Twin Blades (for reduction piercing) or Aether (for sustainability) in a single round. While their Duo Effect is effective and always available for emergencies or true sweeping, this build also proofs Altina/Sanaki versus Aether keeps with Duo's Hindrance, giving them more deployment flexibility. 
• Like most slower Aether Raids Offense carries, however, this variation of Altina/Sanaki is vulnerable to follow-up attacks and would prefer to end or survive all matchups in good standing. Providing outsourced support such as Drive Atk, Flower of Plenty, Flower of Joy, Caduceus Staff, and/or more is advised (and is generally good practice in other Aether Raids Offense strategies, anyway!).
• Main skill combinations therefore are as follows:
  • Twin Blades + Finish + [Bulwark OR Mystic Boost OR Quick Riposte 4]: Twin Blades' extremely quick firing rate synergizes sinfully well with Finish's +5 damage and 7 HP back on Special trigger. Add on your choice of either Atk/Def Bulwark to stack even more damage and healing on top of this, or Mystic Boost for better healing yields and the ability to fight back versus Dazzling Staff effects, and Altina/Sanaki becomes a very stable, sustainable unit overall. Quick Riposte is also a notable option for being a nice source of damage reduction — something Altina/Sanaki otherwise can't have due to their low Speed — and also ensures a quadruple counterhit that can translate to a confirmed kill.
  • Special Spiral + Aether: The long cooldown count of Aether is counteracted by the cooldown cutting effects of Special Spiral and Ragnell•Alondite's acceleration. Special Spiral's fourth variant also adds on damage reduction nullification, so unless Guard effects are present, you shouldn't be missing out on that from forgoing Twin Blades.
  • Miscellaneously, while Altina/Sanaki's default Null C-Disrupt does help against anti-counterattack effects — a dreaded countermeasure versus Vantage users and tanks overall — it can be a rather tepid option since it's otherwise a wasted slot versus other targets. It doesn't help that Mystic Boost 4 also accounts for Dazzling staff units in addition to healing. 
• Atk/Res Unity is a nice default choice throughout all builds to build damage and bulk and, more importantly, reverse any possible penalties in Altina/Sanaki's Attack and Resistance. Finish, however, would be a preferred replacement if you're able to provide it due to its added healing and damage upon Altina/Sanaki's quick Special triggers. Similarly, high-tier Stance skills add on enemy Special delay, which can be handy in battles where the enemy unit can otherwise make a mess of things with a readied Special of their own.
• As usual on an sustain tank especially designed for Aether Raids offense, Atk Smoke and Pulse Smoke are great choices for increasing longevity against multiple enemies or making matchups versus Pulse-stacking teams more comfortable, respectively. To further magnify Altina/Sanaki's damage output and confirm more kills, however, Joint Drive Atk and Atk/Res Oath 4 are perfectly competitive alternatives.
• A Stance, Form, or Ideal in the Sacred Seal finalizes the build nicely as they provide a solid additional form of bulk and power in one Sacred Seal. Quick Riposte or Mystic Boost, as said as options in the B-slot, are also worth considering to close kills more cleanly in 3-4 hits or provide more sustain, respectively.

Weapon: Ragnell•Alondite (+Eff)

Assist: Positional Assist 

Special: Galeforce 

Passive A: Atk/Res Unity / Atk/Def Ideal / Death Blow 4 / Any Initiation-friendly Atk Increase skill 

Passive B: Wings of Mercy / Spd/Def Tempo

Passive C: Time's Pulse / Infantry Pulse / Joint Drive Atk / Even or Odd Tempest / Assault Troop

Sacred Seal: Atk/Res Ideal / Quickened Pulse / Death Blow / Odd Tempest

• Galeforce is a potent Special that grants its user an additional action after triggering, and despite its high cooldown of 5, it comes rather naturally on Altina/Sanaki, given that:
  • Ragnell•Alondite very quickly kills enemies and charges Altina/Sanaki's Special by hitting twice in one strike. Each hit also comes packed with accelerated charging post-refine — thus bypassing the need to sacrifice a skill slot for Heavy Blade unlike typical Galeforce units. If two hits land without any Guard effects active, 4 out of 5 charges necessary to trigger Galeforce are marked off.
  • …and the last point can be easily finished off with one cooldown cutting effect from Time's Pulse, Quickened Pulse, or equivalent ally support (such as Wolfpup Fang, Groom's Wing, Infantry Pulse, or Ostia's Pulse), minimizing the amount of setup Altina/Sanaki requires to trigger Galeforce.
• Galeforce is an initiation Special — meaning that Altina/Sanaki want some initiation-friendly, damage-increasing skills as the passives. Their default Atk/Res Unity is a decent start, but it requires Altina/Sanaki to keep themselves within two spaces of some other ally, which might not always be possible or optimal in some situations. In its place, Death Blow is a simple and accessible substitute, and other higher-rung skills like Atk/Res or Atk/Def Ideal work too as long as they at least give equivalent Atk upon attacking. 
  • The above applies to Altina/Sanaki's Sacred Seal also, assuming it isn't already being occupied by utility skills like Quickened Pulse or a Tempest skill (for increased initiation movement). Death Blow and Atk/Res Ideal are straightfoward recommendations here.
• On Aether Raids Offense Galeforce teams, multiple methods of extra movement and turns are linked with each other to dismantle the opposing Defense in a turn or two. Wings of Mercy, then, will often be Altina/Sanaki's best B-slot option as it allows instant teleportation next to a damaged ally, significantly improving their movement options and the team's general momentum. For combative options, a Tempo skill — preferably an Atk/Def version as soon as that releases (at this time of writing) — is nice to have for charging up Galeforce regardless of Guard effects. 
• Altina/Sanaki's infantry status gives them some nice C-slot options to chew here. 
  • Time's Pulse, again, helps them self-sufficently lower the amount of charges required for Galeforce.
  • If Pulse effects are provided elsewhere, you can opt to help the Special charging of other infantry allies instead by running Infantry Pulse on Altina/Sanaki themselves. 
  • Joint Drive Atk provides another layer of damage for both its user and surrounding teammate.
  • A Tempest skill may often be appreciated due to the extra movement space they provide. Assault Troop also does this, but trades freedom of movement for turn consistency. 

Weapon: Ragnell•Alondite (+Eff)

Assist: Ardent Sacrifice / Positional Assist 

Special: Twin Blades

Passive A: Atk/Res Ideal / Atk/Res Unity

Passive B: Vantage

Passive C: Atk/Res Oath 4 / Joint Drive Atk

Sacred Seal: Atk/Res Form / Atk/Res Ideal / Fierce Stance / Atk/Res Solo

• It's rather agreeable that running Vantage in the B slot can be considered a rather wasteful effort, considering the unit in question has that exact effect baked into a Harmonized Skill command button. Duo's Hinderance being so commonplace in higher tier Aether Raids Defense maps, however, often blocks consistent use of the Harmonized Skill. 
• Therefore, provided you don't intentionally bring Altina/Sanaki to maps with obvious countermeasures (ridiculously high Def enemies, Windsweep, any other forms of counterattack cancellation, etc), you can use them as you would any other Brave weapon + Vantage sweeper. Ultimately, the combination of Ragnell•Alondite and any additional high Atk investments you can offer in the passive slots should serve to knock out enemies in a one-two punch.