Ash

Weapon: Horn of Opening

Assist: Positional Assist / any Rally / flexible

Special: Bonfire / Moonbow

IVs: +Atk or +Def or +Res / -Spd

Passive A: Atk/Def Unity / flexible

Passive B: Lull Atk/Def / any Ruse / flexible

Passive C: Opening Retainer

Sacred Seal: Distant Guard / Drive Atk / flexible

• Ash is an excellent support unit for many teams, largely because of Opening Retainer allowing allies within two spaces of her to teleport within 2 spaces of her. This build attempts to double down on that strength by adding other supportive skills while also maintaining some good combat abilities. 
• Positional assists such as Reposition are generally useful in many contexts. Alternatively, Ash can opt for a Rally skill like Rally Up Atk+ (but any rally works) with a B skill like Atk/Spd Ruse to allow her to apply a stat debuff and the Guard effect when she rallies to any foes in the column she is in and the column her target is in. This effect, particularly the Guard part, can be quite useful to prevent enemy units from activating Specials. 
• The choice of Special is flexible. Bonfire is reduced to 2 cooldown by Horn of Opening, allowing Ash to activate it on her second attack after getting counterattacked under normal circumstances, and Bonfire’s damage scales with Ash’s good Def, making it a reliable option for extra damage. Other specials can be used depending on the needs of the context. 
• The choice of boon is flexible. +Atk is never a bad choice, allowing Ash to deal extra damage in combat and be more likely to be targeted by enemies with Chill Atk, potentially allowing an ally to not be targeted if their Atk is lower than hers. Likewise, +Def and +Res are useful for increasing her bulk in combat and for skill targeting. +Spd may be useful in some particular cases against slow foes with the ability to block her follow-up attacks using skills like Wary Fighter or Maltet; if Ash can activate the guaranteed follow-up attack from Horn of Opening, she then relies on Spd to double. +HP is generally less useful than other boons. -Spd is a relatively safe choice of bane that doesn’t impact Ash’s uses other than against slow foes that block follow-ups. 
• Lull Atk/Def is a solid B skill that debuffs the Atk and Def of Ash’s foes by 3 in combat while also nullifying any visible buffs the foe has in those stats (those from a skill such as Atk Tactic, but not in-combat buffs like from Death Blow). A Ruse may also be a good choice, as mentioned above, or another support option like a chill such as Chill Atk based on the needs of Ash’s teammates. Support skills with an HP check like Sudden Panic or Even Pulse Tie are generally difficult for Ash to use in Aether Raids because she is a Mythic Hero, so all non-mythics on most teams are receiving between 10 and 20 HP from Mythic stat boosts while Ash is not. 
• The seal is flexible, depending on the needs of Ash’s teammates. If she is supporting units that want to take attacks and retaliate against units on enemy phase like Brave Hector, then a seal like Distant Guard can be useful to increase her teammates’ Def and Res against ranged foes. If she is supporting units that prefer to KO things on player phase, Drive Atk or Drive Spd provide stats to help with that. Of course, other options may be better on particular teams.

Weapon: Horn of Opening

Assist: Positional Assist / flexible

Special: Bonfire / Sol

IVs: +Atk or +Def or +Res / -Spd

Passive A: Atk/Def Unity / Distant Stance or Distant Counter / flexible

Passive B: Lull Atk/Def / Wrath / flexible

Passive C: Opening Retainer

Sacred Seal: Steady Breath / Atk/Def Form / Mystic Boost / flexible

• With her great Atk and Def and good Res, as well as the effects of Horn of Opening allowing her to guarantee and avoid follow-ups, Ash can function well as a tank, surviving hits and retaliating with powerful counterattacks. 
• The choice of A skill depends on team context. Ash can stick with her default Atk/Def Unity to improve her matchups with melee units, especially in cases where her Atk or Def are debuffed, such as by Chill Atk, Bright Shrine/Dark Shrine, or a dagger debuff. This is powerful and easy to use if she is used on a team with a unit using A/R Far Save and may be useful on other teams as well. Alternatively, she can use Distant Stance or Distant Counter to counterattack against ranged enemies. 
• The B skill is flexible. Lull Atk/Def is a good option that increases Ash’s damage and decreases her damage taken, particularly against enemies with buffs in Atk or Def. Alternatively, she can opt for Wrath in order to deal an extra 10 damage when she activates her Special. 
• Opening Retainer is a fantastic C skill that allows Ash’s allies within 2 spaces to warp within 2 spaces of her, in addition to the effects of Joint Drive Atk. There is generally no reason to replace it. 
• The seal is flexible. Steady Breath is a fantastic option that increases Ash’s Def by 4 on enemy phase, as well as giving her +1 Special charge on all attacks including her foe’s. This allows her to take one hit and then retaliate with a Bonfire guaranteed as long as she is transformed. Other seals can also be useful, particularly if she is receiving the Breath effect from an ally like Brave Lucina or Summer Hilda; Atk/Def Form gives her up to a +7 boost in Atk and Def if 3 allies are within 2 spaces, which synergizes nicely with the conditions for Horn of Opening, though they do need to be slightly closer. Mystic Boost heals her by 6 after combat, disables Wrathful Staff and similar effects, as well as preventing enemies from targeting the lower of her Def and Res using skills like Sorcery Blade. 

Weapon: Horn of Opening

Assist: Positional Assist / flexible

Special: Galeforce / Bonfire

IVs: +Atk / -HP or -Res

Passive A: Sturdy Impact / Atk/Def Unity / flexible

Passive B: Lull Atk/Def / Wings of Mercy / flexible

Passive C: Opening Retainer

Sacred Seal: Heavy Blade / Sturdy Blow / Atk/Def Bond / Blade Session / flexible

• Ash’s high Atk, guaranteed follow-up, and ally teleportation allow her to deal high damage attacking on player phase, including on a Galeforce team. The effects of Horn of Opening are essential for this build; the lowered Special cooldown allows her to activate Bonfire on her second attack or Galeforce after attacking twice if she is receiving bonus cooldown from an effect like Heavy Blade. If she is transformed, it also neutralizes skills like Guard that would slow her Special activation. However, it only guarantees a follow-up attack if 2 or more allies are within 3 spaces, meaning that Ash has a harder time being the first one to attack an enemy formation across the map. For this reason, it may be effective to use her with Wings of Mercy to allow her to teleport adjacent to an ally below 50% HP. 
• The ideal boon is +Atk, as Ash wants to deal high damage and hopefully KO her foe in one combat. The ideal bane is -Res, but others like -HP or -Spd have generally similar performance. 
• The A skill is flexible. Sturdy Impact increases Ash’s Atk by 6 and Def by 10 when she initiates combat, as well as preventing her foe from making a follow-up attack under normal circumstances. Her base Atk/Def Unity is also a good choice that provides a lesser stat boost that isn’t restricted to player phase while also essentially reversing any penalties she has in Atk or Def. Other A skills may also be better depending on the particular use context. 
• Opening Retainer is an excellent C skill, allowing Ash’s allies within 2 spaces to teleport to any space within 2 spaces of her, providing great movement flexibility. In addition, it also includes Joint Drive Atk, boosting her Atk and the Atk of her allies within 2 spaces by 4 so long as there is at least one ally within 2 spaces. In certain cases, it could be worth replacing with Time’s Pulse if this allows Ash to activate Galeforce after a single attack, but in general Opening Retainer is highly useful and there is not a strong case for replacing it. 
• Heavy Blade is an excellent choice of seal that boosts Ash’s Special charge by 1 on her own attacks so long as her Atk is higher than her foe’s, which other skills like Lull Atk/Def help with. This extra Special cooldown is important to the functioning of this build. If she is receiving cooldown from another source such as Infantry Rush, then other seals that boost her Atk and Def like Sturdy Blow or Atk Def Bond may be useful.