I HAVE THEORIES!! Get out your corkboards and red string!
1) WE ARE THE SECOND EMBER! Thats why our story seems to take place alongside the other Kids. Like at the same time as they are doing what they do in the films.
2) This special memory container isn't just a memory it's a time machine. Proof? The "memory" isn't blue or transparent, we CAN lose wing light from the crabs, we are placed directly into the event, and we can interact with everything in the environment. We might not have our powers but thats probably why we can't change their fates.
3) THE SOLDIER STORY DIDN'T END. proof? I think Tsadi, The Wasteland Elder, RECOGNIZED us when we met him. I think this was his second time meeting us. Thats why he just stares at us so gently. He was watching someone from 500 years ago helping him again and didn't want to scare us knowing how much he had changed. Not knowing this was our first time meeting him. Proof?
4) He has the same shield and specialized in the spear. only issue with this one is the dominant hand but that COULD just be an old war injury forcing him to have to switch which side he fought with. He is pretty hurt when we meet him as the Elder.
5) I think we recognize him when we are in the past. Especially with how much we attempt to help him and fight along side him. Hoping we can save everyone. we keep glancing over at him as if we feel like we've seen him before. Especially while he is comforting the Manatee.
I realize how corkboard crazy this all might sound, especially the time machine part, but DUDE I might be onto something here. Definitely might make this at least my own personal headcannon.