An escape ring D'Nadia carries that is rendered worthless by the standing teleportation ban during the fight.
Princess Donut lists it among Empress D'Nadia's gear when briefing Carl on the way in, noting flatly that it is useless now — the ban on teleportation and phasing means the empress cannot ring out of The Throne Room no matter how badly the fight goes.
Its uselessness is the structural reason the chapter can happen at all: a warlord who could teleport to safety could never be pinned down, stripped of shields, and marked.
A ring worn by the empress, dead weight under the current ruleset.
D'Nadia's escape option, neutralized by the teleport ban.