Dark Souls Remastered | Redeeming a Fire Keeper Soul

This is not a necessary item, but it is very useful. The Fire Keeper Soul I get here is in the Duke's Archives and I redeem it with the girl in the cell below Firelink Shrine.

"This soul is used to reinforce Estus Flasks, to increase its healing powers.

To improve your Estus Flasks give the Fire Keeper Soul to one of the three Fire Keepers: Anastacia of Astora, the mute girl in the cell below Firelink Shrine, the Daughter of Chaos (Chaos Servant leader in Quelaag's Domain) or the Darkmoon Knightess, the brass armored Fire Keeper in Anor Londo."

Source:

https://darksouls.wiki.fextralife.com/Fire+Keeper+Soul