A vampire with no circle designation is in his own unique circle. Vampires with the same name (eg. The Embrace, non-unique vampires) do not share a circle by default, each has his own circle of one by default.
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Walk of Caine
Only usable as a bleed action is announced. Choose X ready Blood Brothers you control with 1 or more blood of the same circle as this Blood Brother, including this Blood Brother. Each chosen Blood Brother burns 1 blood. +X bleed (limited).
As above, but usable any time before the action is resolved.
Rulings
Must be played (as well as other "as the action is announced" action modifiers) before action modifiers that are not explicitly played "as the action is announced" (e.g., Conditioning).
Replace the action card (if any) before playing it.