The Knight's Corpus
The Knight's Corpus is a Collectible in Mizuki & Caerula Arbor.
Resisting does not come without a price. The knight's body had long since become riddled with wounds, but he paid no heed. He will fight until the bitter end, even should his body be smashed to pieces.
Effect
Reduces The Last Knight's DEF by 80% (from a grand 4000 to 800), making "Fate's Favored Child" (and by extension, reaching the Age of the Silence ending) much less difficult. However, be wary that the Tide-Hunt Knight will be affected as well, reducing his DEF from 1000 to 200!
Acquisition
The Knight's Corpus may be obtained from Encounter: The Knight Persists, which will only appear when the player has the 
Breath of the Tide, by choosing "Break free".
Since Encounter: Delusions of Lunacy where the the Breath of the Tide is obtained will only appear in the following runs after the player had completed a run, it is impossible to obtain The Knight's Corpus before then.