Here's a copy of some extra info I tossed up on spacebattles:
I chose this scene as a test snip because it had more known characters. The story starts from when he falls into Creation, so we get six months of solo Shirou, and six months of Solo Shirou dodging Rin and Saber once he realizes they came after him because he's not exactly proud of some of the things he was coerced into doing/becoming for the Reclamation before he had complete information.
General ideas/plans:
Ligier can be a pretty persuasive guy when he tells you to kill someone for the greater good.
Shirou's introduction to and gradual/inevitable falling out with the forces of Malfeas once he realizes they are actually jerks sort of encapsulates the whole first bit of the story. The charms he took and the way they changed him during a period that he honestly didn't think he would ever see Rin and Saber again have altered some bits of his personality - but not in any drastically shown way here.
Third circle demons in Exalted are smart, but there are only so many ways you can manipulate a person that 'tries to save everyone' into destroying shit before he catches on.
Rin and Saber sort of lampshade the "EVERYONE GETS AN EXALTATION LOLOLOL" nature of Exalted crossovers. Saber gets exalted as a Zenith roughly forty minutes after arriving in Creation, because she is more or less the incarnate textbook example of such. Rin earns her lunar exaltation shortly thereafter, much to Luna's personal amusement. Saber changes the least initially, and Rin still relies on thaumaturgy for a good while before finally embracing her proper Lunar abilities. That the economics of Creation (and the South) allow for easy access to 'non magical materials' like gems relatively cheaply, and that as an exalt she can charge up said gemstones much faster than she ever could as a mortal on Earth sort of monopolizes her attention outside of the hunt for Shirou initially; she can actually afford to waste gems on experiments and advance her craft faster than she ever could back home. Once she makes a few leaps and bounds in the fields she had been dedicating a life's work to before, she turns her attention to her new nature . . . and its side effects.
Her motivation might waver between 'Find Shirou' and 'Conquer Gem' during those first months after she arrives.
Obviously it's been the proper ten years since the end of FSN, but I have the cast changing only a little bit. Rin's been running a ten year campaign on Shirou to loosen him up and get him to relax, and Saber helps in that regard. Saber has actually chilled out a bit more than Shirou seeing as her original ambitions are literally out of reach while she's here on her 'vacation' with the two of them. Once she gets her Exaltation, it's a tiny bit of a religious experience (Zenith, after all) and she is severed from her contract with Gaia/Alaya. The UCS gives her a divine pat on the head, calls her a good girl, and says she she is allowed to let go; she is granted a properly materialized flesh body and can now grow into and beyond puberty (rapidly, by dint of Exaltation).
Once Shirou is cut off from them he backslides hard into self-sacrificing heroics, initially out of guilt over the Sakura incident but he continues because it's more or less natural for him. This clashes with the mindset of the average Infernal, and he spends a decent amount of time failing to fill the rather large and tyrannical shoes of the Slayer that previously held his exaltation. The 'team' he's initially encouraged to work with assumes he will maim them for the slightest backtalk because that's how his predecessor rolled; by the time that coven realizes he's not that kind of asshole, they realize he's also not exactly warming up to the SOP of 'indulge and be a rockstar from Hell when you aren't on duty.' He may accidentally inspire some Infernals in a positive manner without meaning to during his time in Malfeas.
As he matures as an Exalt he has to reconcile his missions with what he thinks is right, and he also quietly feels his power growing in ways that he was not told to expect; Avalon had something to say when he initially got Chosen and its voice was muted but not extinguished when his soul was being renovated. As such, he's gating early into heretical and devil-tiger charms (Exalted jargon for 'unique flavor' instead of 'one of the big 6 demons flavored') and incorporating his personal sword thematics quite strongly. While his demonic bosses are okay with his lapses into heroic behavior here and there (All he's doing is setting himself up to be disillusioned! When he snaps he'll be the perfect agent!), they are much much less okay with him once they notice his growth into something outside the proper design spec for his granted power, and he quickly becomes a liability. When he shows his hand by refusing to die when killed (haw haw) and invoking the limits of his as-yet-unrevealed-to-hell power, he goes from liability to Active Threat to the Reclamation and becomes a high priority for extermination; mostly because if he can cheat and grow beyond his limits, he can teach the other Infernals to do the same.
That all seems spoilery as hell but it's really just the basic heartbeats of the themes I'd be trying to hit.