Millennium Castle Brunestud

Millenium Castle Brunestud
千年城ブリュンスタッド

A castle created by the most powerful True Ancestor ever through the Marble Phantasm ability and not the original creation of Arcueid. The first master of Brunestud has already been annihilated, but since then, those True Ancestors able to form it were treated as the royalty. True Ancestors, beings that have no concept of social stratification, call her the princess for this reason.

Existing in the location closest to the moon, not topographically, but where the world receives the most influence of the moon. Even without Arcueid around, the castle is still seemingly in existence, but without "life". To the True Ancestors, the castle was probably their absolute protection.

Also described in Tokuhon as being a Reality Marble. Further, going by the hanafuda game in hollow ataraxia, inheritence of a Reality Marble IS possible. A Reality Marble that's really the Crimson Moon's, manifested by using the Marble Phantasm ability?