Restoration (修復 Shūfuku) is the act of using Power of Existence to adjust the discrepancies of the causality of the space inside a Fūzetsu, which has been severed from the causality outside, to match the flow of causality outside of it.
By doing this, it is possible to restore anything that has had its causality severed within a Fūzetsu, be it a living being or an object, to the state that it was in before its causality was severed.
Background[]
A principle of Restoration is that if someone's causality is not severed within a Fūzetsu and they can still move, they can't be restored even if converted into Power of Existence because the causality they would be adjusted to match to had already left the world.
Along with concealment, Restoration is one of the biggest advantages of the Fūzetsu, as it allows Crimson Denizens and Flame Haze to still remain unknown to the world in the modern era, when it would have been more difficult to remain in the shadows with the population increase and technological advancements of humans. Flame Haze often use Restoration to suppress the damage from battles, but Denizens may also use it if needed.
As it is a function of the Fūzetsu, Restoration is seen as one of the most fundamental Unrestricted Spells. Normally, it is carried out using the Power of Existence of Torches in the area, but if there aren't any around, Flame Haze would use their own Power of Existence.
If not enough Power of Existence is applied, restored buildings would be weak and crumble or signs of damage would still be subtly present.[1]
Two Treasure Tools, Tendōkyū and Seireiden, have the capability of automatically restoring damage.