Captain Marvel #31, aka Captain Marlo #1.
This issue finds Marlo Jones on the brink of death, with her life literally flashing before her own eyes–and the eyes of the reader. We see her old interactions with Mr. Fixit, how she met Rick Jones, etc. All in flashback, so characters who appear only in those sequences are not tagged.
I don’t think we’ve ever seen a side character get a full “origin story” (of sorts), and few comic book writers can do character work as well as Peter David so this makes for a solid read.
At issue’s end, Captain Marvel finally returns from this mission against Maestro in the prior arc.