Not much is known from the Hunters of Hunters, only that there is only but one, per generation, and they are must abide by ancient oath to slay the hunters who would turn on their duties and become the very things they hunt.
Eileen the Crow, the bearer of this oath, in this generation, is an old yet skillful woman who eventually passes on the torch to the player.
Because of the intoxication of Blood among Yharnamites. Traditionally, the Hunter of Hunters are outsiders.
While bearing the rune of the Hunter of Hunters, one may be summoned to another world through the Small Resonant Bell, to the world of a "Blood-Addled" Beckoner as a purple adversary. This seems to be linked to the unlawful murdering of NPCs, though details are yet unbeknownst. Two Purple Adversaries intruding in the same world are Non-hostile to one another, though can interact with regular Adversaries.