Image: Rebel Wolves / Bandai NamcoOfficial screenshot from Rebel Wolves / Bandai Namco.
The Dark Mistress is a hidden story achievement tied to Xanthe, one of Brencis's lieutenants. You earn it through the main quest, and how you resolve it is up to you.
The Cycle of LoveThe Cycle of Love is the boss quest for the boyar Xanthe, unlocked once her anger is maxed through court activities. You get into her mansion with a lantern and face her in a locked room.
XantheXanthe is the oldest of Brencis's Boyars. She rules the southeast of Vale Sangora, where she digs up ancient secrets for Brencis's army and raises his Blood Guards.
Xanthe, the Dark MistressXanthe is fought in Svartrau Cathedral at night. Her health bar names her the Dark Mistress. A blood mage Boyar, she is often called the hardest of the court fights, so go in at level 25 or higher.Guides say you can either defeat Xanthe or make a deal with her during The Cycle of Love. Either outcome counts.
Drinking Xanthe's blood afterwards unlocks Blood Surge, which you need for Make It Rain.
Neutralise the threat Xanthe poses.