Many thanks for sharing your in-depth and thought-out analysis of the story. As a philosophy, I try to subscribe to the theory of death of the author: I try to resist the urge to share my reading of my own work (because I don't want it to be taken as the "authentic" interpretation), but I'm very grateful whenever I'm able to get a glimpse of how others engaged with it, whatever their opinion may be. :-)
I will make a very small exceptions in regard to the main character's age because it was something I tried to establish in the text, even if in a throwaway line. The first flashback is stated to take place a few moons before Unagi's coming of age (admittedly a bit ambiguous) and five years before the main story. So Unagi and Cody are meant to be 17 and 23 respectively when they first meet, and 22 and 28 by the end of the story, with the flashbacks taking place at various points within that interval.
That's all I'll say, but again thank you a lot for your analysis, it was deeply appreciated. :-)