Stalwart
This unitUnitUnits fall under 2 categories: party and enemy. These 2 categories, in relation to one another, are referred to as opposing units. cannotCannotIf a component's effect uses the word cannot, that effect cannot be overruled by another game effect. lose more than 1 HP in a single turnTurnDuring a battle round, each unit on the battle map takes a turn. Some abilities are limited to a certain number of uses per turn; that limit is reset at the start of each unit's turn..
How does Stalwart work?
If a unit can't lose HP, for example by having the enemy skill Stalwart, nothing can cause it to lose HP. This includes true damage. This isn't damage prevention like defense is, so no type of damage can override this. Only skills/abilities that would straight up defeatDefeatedA unit is defeated when it loses its last HP chip or an effect states that it is defeated the unit outright can get around this (or the FearFearThe effects of this unit's non-Combat skills are ignored. This effect does not apply to skill dice already in active slots or the cooldown track. status effect, which would then allow you to ignore the skill entirely).
SourceHow does Stalwart and Master Blastbones work?
Stalwart is only applicable to HP lost in a unit's turn. It doesn't apply for damage dealt outside of a unit's turn, such as damage dealt by the companions summoned through Master Blastbones.
Source