This is Elieen the Crow. She is probably my favorite character in Bloodborne, both in appearence and actual character.
Her crowfeather garb probably is my favorite torso piece in the game. The "wings" offer a very pleasing aesthetic, especially when in rapid movement. It also has some pretty good in-game stats as well, and although you can only aquire her clothing (and amazing weapon) in the later game.
Her mask though is the crowning piece, at least in my opinion. It alludes back to the the medieval plague doctor masks, which fits perfectly into the theme of Bloodborne. The whole game (especially the beginning) has a very imposing atmoshpere of sickness and a plague ravaged city.
Her weapon is also probably my favorite to use in-game. The Mercy Blades are practically completely skill based, and can't be buffed, yet remains remarkably potent. It's only reaches its maximum potential with very high skill and stamina, as the weapon's attack rate increases with consecutive attacks, allowing you to stun lock opponents and rack up ridiculous damage.