Fire Keeper Soul

In-Game Description
''Soul of a long-lost Fire Keeper. Each Fire Keeper is a corporeal manifestation of her bonfire, and a draw for the humanity which is offered to her. Her soul is gnawed by infinite humanity, and can boost the power of the precious Estus Flask. Reinforced Estus Flasks capture denser Estus, allowing for increased restoration of HP.''

The Darkmoon Knightess' soul:

''Soul of the Darkmoon Knightess, Fire Keeper of Anor Londo. A Fire Keeper's soul is a draw for humanity, and held within their bosoms, below just a thin layer of skin, are swarms of humanity that writhe and squirm. Her brass armor serves to disguise this ghastly form.''

Anastacia of Astora's soul:

Soul of the Ash Maiden,'Fire Keeper of Firelink Shrine.'A Fire Keeper's soul is a draw for humanity,'and held within their bosoms, below just a'thin layer of skin, are swarms of humanity'that writhe and squirm.'Was the Ash Maiden locked in this dark prison'for some transgression, or by her own will? Quelaag's Sister's soul: Soul of a Daughter of Chaos,'Fire Keeper of Quelaag's Domain.'A Fire Keeper's soul is a draw for humanity,'and held within their bosoms, below just a'thin layer of skin, are swarms of humanity'that writhe and squirm.'To her, the countless eggs which appeared'were cradles for each tiny humanity.

Usage

 * Can be consumed, the Fire Keeper Soul will grant the user with 5 units of Humanity, and restore full health. Consuming is not recommended because of its limited benefits (unless you have +7 Estus Flasks, as it is the maximum), while upgrading flasks provides permanent benefits.
 * You can Give the Fire Keeper Soul to one of the three Fire Keepers: Anastacia of Astora below Firelink Shrine. Quelaag's Sister in Quelaag's Domain. Or Darkmoon Knightess at the main bonfire in Anor Londo. to reinforce Estus Flasks, to increase its healing powers (but not the amount of estus you can carry).

Locations

 * One is located in Undead Parish. It is on an altar in the Undead Church, guarded by a Tower Knight.
 * One is located in New Londo Ruins. It can be seen on the right hand when crossing the narrow wooden walkway. Three ghosts will spawn when getting near.
 * One is located in Blighttown. In a wastewater pit, guarded by fire-dogs and poisonous dart shooters.
 * One is located in the Duke's Archives. At the bottom of the prison tower, behind the octopus-headed monsters. Need the Archive Tower Giant Cell Key that is acquired later in the level, do not confuse this with the Archive Tower Giant Door Key.
 * One is obtained after killing Quelaag's Sister. Please note that you won't be able to join the Chaos Servant covenant or use the bonfire in front of her anymore (with the exclusion of being able to warp to, but not from, that location).
 * One is obtained after killing Darkmoon Knightess in Anor Londo at the first bonfire. If you decide to kill her for her soul, her bonfire will no longer be lit but you may still warp there using the Lordvessel.
 * One is obtained off Lautrec of Carim in Anor Londo after he kills Anastacia of Astora. Players may choose to either return the soul to its owner, restoring the Firelink Shrine bonfire, or choose to use it otherwise.

Trivia

 * The FIre Keeper Soul obtained from the Darkmoon Knightess has a unique game description. It is, however, functionally identical to the other Fire Keeper's Souls.