Still with me? Cool.
So I was thinking, at the end of the main quest when you defeat Alduin, you do not absorb his soul. Paarthunax and Arngeir both speculate that this is because Alduin is not truly defeated, and will one day return to fulfill his destiny and role as the World Eater. That got me thinking, what if the reason you didn't absorb Alduin's soul is because you already have it? As a dragonborn, you have a mortal body and the soul of a dragon, so what if the Last Dragonborn is in fact the reincarnated soul of Alduin? If that's the case, a Dragon Break would have had to occur when you were born that allowed you to be born with Alduin's soul, since he wasn't killed at the time of his defeat and didn't exist again up until his return in the Fourth Era.
This idea would allow both characters, the Last Dragonborn and the World Eater, to fulfill their destinies, since after you die your soul will be released (barring any unforeseen Soul Trap spells, although those probably won't work on you since the spells don't work on dragons) and be free to reincarnate as Alduin once again, and since the Last Dragonborn no longer exists, Alduin will be able to fulfill his purpose (generally) unopposed.
So that's my theory. Obviously it can't be tested at all, but I think it makes sense and would be an interesting development for the character.
Thoughts?
