The Blades are an organization in the Elder Scrolls games. Initially, they were dragonhunters from Akavir who came to serve the Septim emperors as bodyguards and agents. When the Septim dynasty ended at the end of Oblivion, the Blades briefly sought to defend the empire from outside influence (the Aldmeri Dominion), then went into hiding until a new Dragonborn appeared.
As we see in Skyrim, the Blades have retained their initial opposition against dragons from centuries past. I find it odd, then, that they would support the Dragonborn - a human with the soul & abilities of a dragon.
If the Blades hate dragons, why do they hold the Dragonborn in such high esteem?