A manifestation of a certain will in Ursus. The most terrifying military force in the entirety of Ursus, they are widely-known throughout the world only as horrifying spectres of legend and yore. A single one is enough to slaughter entire squads. Defeat has never been a possibility.
Two fearsome spectres clad in uniform, observing Talulah with keen interest. Permanently applies [Weaken] to Talulah, the Fighter (Greatly reduces DEF and RES).
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—Tooltip
Despite being technically considered as a boss enemy, the Emperor's Blade is more of a hazard; they are invulnerable, does not attack, cannot be blocked, and will despawn by entering Incursion Points after some time has passed from when they spawn, which does not cause the player to lose Life Points.
The Emperor's Blade's only purpose is to debilitate Talulah, the Fighter by applying a permanent Weakendebuff which halves her DEF and RES that they will use (and only use) 7 seconds after spawning.