Add a subrule to “Relics of Power” (or “Relics” if the rule has been renamed), called “The Weakness”:-

The Dark One may have a Weakness, being a noun which exists in the dynastic ruleset of a past dynasty, and which is a kind of weapon or kind of tool. The Dark One privately tracks their own Weakness.

If the Dark One has no Weakness, he may select one by making a Story Post naming the Stratum of the Dynasty whose ruleset this Weakness appears in and the first letter of this Weakness, and updating his Weakness accordingly.

If the Dark One has no Weakness, he may not take dynastic actions outside of this rule, nor pass the mantle.