Oath of Ostia

Type	Icon	Name	SP	Required	Description [ExpandCollapse]
A		Oath of Ostia	300	—	Grants HP+5. After unit acts (if Canto triggers, after Canto), or, if defending in Aether Raids, at the start of enemy phase, applies【Divine Vein (Stone)】to unit's space and spaces within 2 spaces of unit for 1 turn. If foe initiates combat or foe's HP ≥ 75% at start of combat, inflicts Atk/Def-10 on foe, grants Special cooldown count-2 to unit before foe's first attack, and reduces the percentage of foe's non-Special "reduce damage by X%" skills by 50% during combat (excluding area-of-effect Specials).	Grants HP+5. After unit acts (if Canto triggers, after Canto), or, if defending in Aether Raids, at the start of enemy phase, applies【Divine Vein (Stone)】to unit's space and spaces within 2 spaces of unit for 1 turn. If foe initiates combat or foe's HP ≥ 75% at start of combat, inflicts Atk/Def-10 on foe, grants Special cooldown count-2 to unit before foe's first attack, and reduces the percentage of foe's non-Special "reduce damage by X%" skills by 50% during combat (excluding area-of-effect Specials). 【Divine Vein (Stone)】 Applies the following effects on space for unit and allies: Grants Def/Res+6 during combat, reduces damage from foe's Specials by 10 during combat (excluding area-of-effect Specials), and reduces damage from area-of-effect Specials by 50% (excluding Røkkr area-of-effect Specials). (Divine Vein effects do not stack; replaces any existing Divine Vein effect; Divine Vein effects applied simultaneously cancel each other out. Does not count as defensive terrain.)
This skill can only be equipped by its original unit.

* Unused restrictions: No restrictions.

Effects[ | ]

Effects	Targets	Conditions
Permanent effects
HP+5	Unit	—
Map effects
【Divine Vein (Stone)】	Spaces within 2 spaces of Unit	After action(s), Canto movement, or at start of Enemy Phase when defending in Aether Raids
Combat effects
Atk/Def-10	Foe	Enemy Phase or Foe's HP ≥ 75% at start of combat
Reduces the effect of "Reduces damage by X%" by 50%	Foe
Special cooldown count-2 before Foe's first attack	Unit

Notes[ | ]

【Divine Vein (Stone)】 adds effects to spaces regardless of the terrain of those spaces.
- Divine Vein effects do not stack with each other. if a Divine Vein effect is applied to a space where another Divine Vein effect is active, the previous Divine Vein effect is overwritten.
  - Divine Vein effects applied at the same time cancel each other out, leaving the overlapped spaces without a Divine Vein effect.
- Divine Vein effects do not apply to spaces with unbreakable walls, unbreakable structures, and other unbreakable terrain.
- 【Divine Vein (Stone)】 is not considered defensive terrain, so Queensblade and Breezy Spear will not disable it's effects.
- The Def/Res+6 that can be applied by 【Divine Vein (Stone)】 is considered a temporary buff.
- The damage-reduction effect is a flat -10 damage that is calculated after offensive Specials, damage boosting effects such as Arcane Lúin and Dominance, and "reduces damage by X%" effects such as Gust and Dodge.
  - If a skill such as Miracle or Everliving Domain can trigger, the damage-reduction effect will not trigger and the user will still survive with only 1 HP.
  - Flat damage-reduction effects stack additively, similar to interactions related to the weapon-triangle, such as Triangle Adept and the weapon-triangle advantage boost.
  - Flat damage-reduction effects cannot be neutralized or reduced by effects such as Share Spoils or Halves non-Special damage reduction.
  - For more information, see Damage calculation.
- The damage-reduction effect is calculated after offensive Specials and damage boosting effects such as Arcane Lúin and Dominance.
  - If a skill such as Miracle or Everliving Domain can trigger, the damage-reduction effect will not trigger and the user will still survive with only 1 HP.
  - "Reduces damage by X%" effects stack multiplicatively, unlike interactions related to the weapon-triangle, such as Triangle Adept and the weapon-triangle advantage boost.
    - For example, if both Dodge and Gust trigger, the maximum total damage-reduction is 64% instead of 80%, since the two skills reduce the damage to (1 − 40%) × (1 − 40%) = 36% of the original damage.
  - Non-Special "reduces damage by X%" effects can be neutralized or reduced by effects such as Share Spoils or Halves non-Special damage reduction.
  - For more information, see Damage calculation.
"If foe initiates combat" means if a foe triggers combat during the enemy phase. The unit being initiated upon does not need to deal damage, nor be able to counterattack.
- However, if the effect is applied after combat, the unit being initiated upon must also survive it to fulfill this condition.
Oath of Ostia's Special cooldown count reduction that occurs during combat is a flat -2 and is not affected by effects related to Special cooldown charge such as Guard, Special Cooldown Charge +1, and Spd/Def Tempo 4.
- All flat cooldown count increases and/or reductions during combat will stack with each other if they trigger at the same time.
  - For example, if a unit has Preempt Pulse and Hush Spectrum, the effects will stack and the unit's cooldown count will neither increase nor decrease.
Oath of Ostia will reduce the effect of non-Special "reduces damage by X%" effects from Specials such as Vital Astra.
- Damage-reduction reducing effects stack multiplicatively, unlike interactions related to the weapon-triangle, such as Triangle Adept and the weapon-triangle advantage boost.
  - For example, if a unit has Halves non-Special damage reduction and a foe with Dodge is on a space with 【Divine Vein (Water)】, the maximum total damage-reduction is reduced to 10%, since the two effects reduce the damage to (1 − ((40% − 50%) − 50%)) = 90% of the original damage instead of 60% of the original damage.
- Each damage-reduction effect is reduced individually.
  - For example, if a unit has Halves non-Special damage reduction and the foe has both Spurn 4 and Dodge, the maximum total damage-reduction is reduced to 40%, since the two effects reduce the damage to (1 − (50% − 50%)) × (1 − (40% − 50%)) = 60% of the original damage instead of 30% of the original damage.
- Oath of Ostia will not reduce the effect of Special "reduces damage by X%" effects such as Gust or Laguz Friend 4.
- For more information, see Damage calculation.