I don't know, that will take some time, but Henri did it faster. If it's Sullivan, he might have used to be the right hand, but now he is currently one of the three greats, which means he has some equals within the circle. Plus, it's Delkira's crest, which holds immense power, and they're allowed to use it without Delkira. (I think there would be meetings after meetings if they ever needed to use it, and there are conditions that must be met, like with the royal one.)
Anyone who has that must be holding a considerable amount of power to rule the Netherworld. I'm curious about the limitations of its use, and who is currently holding it (because if the crest falls into the villains' hands, they could abuse it, right?).
Or maybe I'm just overthinking.
I wonder how they got Delkira's crest. I'm so curious. Also, good job, everyone! They were put in the spotlight at the right moment: Fenrir, Iruma, Mephisto, Amy, Nova, and then Henri.