Back Alley Alliance

A congregation of heroines forced to live in back alleys. Right now, Yumizuka Satsuki and Sion are the only official members, though sometimes White Len stops by as well.
In Tsukihime, back alleys were a terrifying place full of corpses, where girls that should have been dead chased you down and cornered you, and classmates hid their blood-drenched arms. However, it seems that ever since the BAA was founded, safety in the alleys has improved remarkably.

MB Act Cadenza PS2 Manual: Tsukihime Dictionary