Brunestud

Despite being Arcueid's last name, strictly speaking it is actually more like a title.
It is possessed by all of the members of True Ancestor royalty.
The Millennium Castle Brunestud where Arcueid had sealed herself away is not her original creation, but was actually created in the past by the most powerful True Ancestor, using marble phantasm.
The original lord of Castle Brunestud died long ago, but ever since the True Ancestors capable of forming the castle have been uplifted as royalty.
This is why the True Ancestors, who have no concept of hierarchy, nevertheless call Arcueid their princess.
After being tricked by Roa and killing most of the True Ancestors, Arcueid crucified herself on the throne of the castle she materialized herself. A thousand chains stretched from the castle's outer walls to the throne, so that she may seal herself away forever.

Tsukihime Data Collection: Tsukihime Dictionary
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Despite being Arcueid's last name, strictly speaking it is actually more like a title. It is possessed by all of the members of True Ancestor royalty.
The Millennium Castle Brunestud where Arcueid had sealed herself away is not her original creation, but was actually created in the past by the most powerful True Ancestor, using marble phantasm. The original lord of Castle Brunestud died long ago, but ever since the True Ancestors capable of forming the castle have been uplifted as royalty. This is why the True Ancestors, who have no concept of hierarchy, nevertheless call Arcueid their princess.
After being tricked by Roa and killing most of the True Ancestors, Arcueid crucified herself on the throne of the castle she materialized herself. A thousand chains stretched from the castle's outer walls to the throne, so that she may seal herself away forever.
In Melty Blood, the Tatari Arcueid materialized the Millennium Castle. Later, in Re-ACT, it also appeared in her Arc Drive.
Currently, there are only two bloodsuckers with the name of Brunestud: Arcueid and Altrouge.

Tsukihime Dokuhon Plus Period: Tsukihime Dictionary Revised