[Acolyte]

Dead Superiors-- I like the Tribe a lot, and it not having been filled might point to the general displacement of indigenous family-unit-based political entities by largely city- and nation- based ones (either as a cause or an effect). Inspiration would have been a very Earth-focused (or at least Vale of Dreams-focused) Word, because it requires lots of contacts with humans; this could explain why the Elder was killed in the Crusade, and it remains unfulfilled because it fits into the Wordsphere of several other Elders you have, all of which might have simply moved in to take what they needed from it and left the Word itself free as a reminder (like Raphael in canon Heaven, whose sphere of Knowledge was absorbed by Destiny, Lightning, a little Creation, and a little Fire, with the rest falling to Raphael's previous Servitor Sophia). A few other possible Words might be Heroism (or just Deeds), the Story (which probably would have been refilled), or Pride (definitely killed by the Purity Crusade). It might also be interesting to have a Grey who went bad and needed to be put down by the rest of the Elders (as happened with Legion and Makatiel). Loki's a classic example (I don't know where he is in your heretical setting), but anyone holding a Word like Trickery or Cunning or Deceit (or better yet, Conceit, with its literary implications implying the framework for a story) might be liable to turning into a bad apple.

Legend-- Since this Elder might or might not be a manifestation of the Symphony (like Yves and Kronos), you might go with something even older and Marches-related; Primus, Aetherius, Origin, or Font. And this being doesn't have to be on the power level of Yves or Kronos; even as a manifestation of the Symphony, it would be through the lens of the Marches (remember, God created a world where the dreams of trees and mountains and later animals and humans CREATED new beings with their own motivations), which is far more obsessed with the accumulation of vibrant and vivid stories, not getting souls to one place or another. This Elder might be limited by his ability to know potential Legends for only great (or destined-to-be-great) people (leaving the weaker Legends totally outside of the realm of his insight and making his insight focused on people Heaven and Hell are likely to already focus on), his inability to leave the Marches, the fact that he changes as the Marches changes, or something like that. Perhaps he does get killed and the Marches just respawns him (Who's to say that that wouldn't be the case for Yves and Kronos), perhaps slightly different (like the Doctor *grin*).

"Roc" dissonance requirement ideas-- Kill an Ethereal, perform violence against an Ethereal, allow a story to go untold, take a set of Ethereal-appropriate vows, allow an angel or demon in the Marches to go unpunished, fail to defend something they have sworn or were assigned to protect, etc