Rosaria's Fingers is a covenant in Dark Souls III focused on rebirth and offering Pale Tongues. Joining this covenant can impact other questlines, specifically Sirris of the Sunless Realms. Players can join by interacting with Rosaria, Mother of Rebirth. Be aware that offering a Pale Tongue to Rosaria will break Sirris's questline, so plan accordingly if you wish to complete both.
Joining Rosaria's Fingers
To join Rosaria's Fingers, locate Rosaria, Mother of Rebirth. Once you have found her, you can pledge allegiance to her covenant. The primary offering for this covenant is the Pale Tongue.
Impact on Sirris's Questline
A critical detail for players is the interaction between Rosaria's Fingers and Sirris of the Sunless Realms' questline. Giving even one Pale Tongue to Rosaria will cause Sirris's questline to terminate. If you intend to complete Sirris's storyline, it is advised to do so before offering any Pale Tongues to Rosaria. After Sirris's questline is complete (e.g., after she is dead), you can safely proceed with Rosaria's Fingers without further consequence to Sirris.
Leonhard's Questline
Leonhard's questline also intertwines with Rosaria's Fingers. After reaching the Anor Londo bonfire, return to Rosaria's Chamber. You will find the Black Eye Orb in front of her. This item can be used to invade Leonhard in the room above Aldrich's bonfire, allowing you to defeat him. This part of Leonhard's quest cannot be accessed without first offering at least one Pale Tongue to Rosaria.