Thanks! I think "The Transient and the Eternal" is actually among the least canon-dependent fanfiction I've written... which is odd, since its main purpose is to explain and/or fill in holes and inconsistencies in Kaori Yuki's manga! But I guess that, partly because it's all pre-canon backstory or post-canon continuation, and because I am trying to make my explanations coherent and plausible, I have to do a fair amount of scene-setting and character development, as it were, rather than rely on readers' memories of any particular scene in canon.

It's interesting to write this trio, because while we see Setsuna interact extensively with both Sara and Kira/Lucifer in canon, we only see Sara interact with Kira once, at the very beginning before any weirdness disrupts their lives. She's briefly in the same scene with Lucifer near the very end, but that's in the middle of a battle, she's crazy for part of it, and Lucifer is preoccupied with telling Setsuna to sacrifice him in order to kill God. So I am extrapolating a LOT based on the easy familiarity they all three show in that one trio-interaction, a couple of "photographs" showing the three of them in happier times, and my understanding of their personalities. I'm glad my results are working for you so far!