Xanthe's Blood Guards are looking for fresh recruits. They offer people a taste of undiluted vrakhiri blood, hoping to get them hooked on it. I should put an end to this.
Stop the recruiters and deal with the blood reliquary
The quest marker is near Silty Mug Inn Shrine, south of Svartrau City in the northeastern Silts. Xanthe's Blood Guards are recruiting people by offering undiluted vrakhiri blood; the journal objective is to stop the recruiters and put an end to that supply.
After dealing with the Blood Guard recruiters, speak to the Blood Addict near the reliquary. The encounter can end peacefully or in violence. When the reliquary choice is available, taking the blood and destroying it lead to different rewards, even though the journal can use the same completion account.
The three completion branches each grant 100 XP and 1 skill point. A peaceful resolution adds 200 denarii. The branch that takes the blood instead adds a Phial of Ambrus’s Blood; destroying the reliquary does not award that phial. The money and phial are not a single guaranteed reward package.
Consuming the Ambrus phial grants its associated vampire ability and increases Corruption. If that unlock is your aim, choose the blood pickup when offered and confirm the phial in your inventory before leaving. Do not assume destroying the reliquary also collects its blood.
Just a Bit More is one activity in Xanthe's recruiter thread. Taste of Power and Come Home have their own markers and blood rewards; completing one does not mean the others have been cleared.