We all know Reman Cyrodiil, Hjalti Early-Beard, Ysmir Wulfharth, Miraak and the player character are/were Dragonborn.

But the Akaviri Blood Seal in Sky Haven Temple was consecrated by Reman II. I'm assuming this implies that he was Dragonborn. Also, the Blades whole purpose is to serve the Dragonborn.. why would they follow around the Emperor and the character when they are not the same?

Anyways.. I've seen a lot of misinterpretation of MK's comments about Alessia and the non-hereditary statement within the Book of the Dragonborn. Dragonblood = Dragonsoul. The emperors seem to have been able to absorb souls like dragons, should the opportunity have arisen.