Edina's theory
So, this was just a passing thought of mine. But while Key was learning to tame his dragon, Sugoi points out how difficult it was to tame a Living being, and while I took it at first as if the dragon was a representation of Key's power, I don't think it's completely off the bat that Key's tama is a living being, and so, different in comparison with how the other tamas work
Where does this leave Edina? All we knew surrounding the incident behind her death was that her dragon was out of control and she died saving other people from it, but it struck me as odd because if Edina was everything Sugoi showed Key, then she should've had full control of it.
Now, while we don't have a lot of info on what the shadows that took Falco's tama are, I do think it would make sense if Edina went back to the school, and it took her tama from her, but because it was not a normal tama, the result was that the dragon couldn't be controlled by Edina anymore and got released, and so Edina sacrificed herself because the dragon would only go away with her death
Might be stupid, but I wanted to put this somewhere