Valtr, The League, and the Vermin
The Beasts and the Kin. These are the two types of enemies that we face in Bloodborne. One is born of the Scourge of the Beast, humans tainted from the influence of the Old Blood. The other are ascended humans, who have purged their body of the Scourge and have become Kin of the Cosmos, pure beings. There’s something else though, some strange third thing that seems to be right around the corner, yet somehow avoid description. It’s almost like there’s something we just can’t put our fingers on, right in front of our nose. To try and pinpoint what this thing is let us examine Valtr, the Beast Eater, and his League of confederates.
We first encounter Valtr in the Forbidden Woods, where he introduces himself to the player. “I am Valtr, Master of the League. Members of the League cleanse the streets of all the filth that's spread about during the hunt. Like any half-decent hunter ought to, you know? Haven't you seen enough of these wretched beasts, freakish slugs, and mad doctors? Sentence these fiends to death.” The League appears to have been an organization that exists during the transitionary period from Gehrman’s workshop into Ludwig’s, however Valtr has been in Yharnam for quite some time.
According to the Constable Garb, worn by Valtr, there is a rather popular fable in Yharnam. “Once upon a time a troupe of foreign constables chased a beast all the way to Yharnam, and this is what they wore. The constables became victims of the beast, except for one survivor, who in turn devoured the creature whole, all by himself.” As Valtr’s title is that of the Beast Eater, it’s very reasonable to assume that he is the constable from this fable. It was when Valtr consumed a Beast, an utterly unholy act, that an Oath Rune was born within him: Impurity.
“This rune, discovered inside the forbidden beast eater, came to symbolize "Impurity," and the oath of The League. Confederates of The League hunt to discover vermin. Vermin writhe within filth, and are the root of man's impurity. Crush all vermin without hesitation.” -Impurity.
When Valtr performed such a tainted act, he gained the Impurity Rune and the ability to see Vermin, and with this ability he formed the League. The League, dedicated to hunting down Vermin, consisted of individuals who were brought face to face with the root of man’s impurity and suffered the consequences. We only know of three confederates, other than Valtr. The first is Yamamura the Wanderer, who is described by his garb as: "Garb of a distant Eastern land, worn by Yamamura the Wanderer. This Eastern warrior pursued a beast for honorable revenge, then became a hunter of the League. But when he stared straight into impurity, it drove him mad." It would appear Yamamura’s membership of the League was rather short-lived, as as soon as the Impurity oath was committed to his memory he was driven mad. So while Yamamura plays a relatively minor role in the League, two more significant figures are the Madaras twins.
From the Butcher Mask, we learn it is a: “Mask of the Madaras twins, denizens of the Forbidden Woods, likely belonging to the older of the two. The twins grew up in silent kinship with a poisonous snake. Eventually they learned human ways, and became hunters. When they discovered vermin even in their beloved snake, the younger brother is said to have murdered the older.” Furthermore, we learn from the Butcher Garb that: “Both the twins became hunters, and brought back and dissected their beast prey, in order to support the villagers in their forbidden research.”