I think I’ve got how to introduce the character who’s giving me trouble. It means going back to an earlier version of him, but a more consistent one.
It helps that in the month between handing SE over to BRAWL and receiving crits, I started writing the sequel. 40,000 words of sequel mean that I’ll have a running start on that draft — and, even better, much of what I’ve put together can be used to patch up SE. It also became clear when I was writing one scene that it really needed to be in SE rather than later . . . and, going by the crits, it’ll be perfect to add about 3/4 of the way through.