So in the stories of Kensei, the dragon took Kensei in and taught him to fight and become the hero of legend... Then the dragon wanted Kensei's love in return, but rather than give her up, Kensei ripped out his heart and gave it to the dragon.
My theory - Hiro is "the dragon"
He turned Kensei into a hero...
Then attempted to steal his love.
Kensei said "you taught me that no blade could harm me, then cut me deeper than any blade ever could" at that point, Kensei became cold and heartless... like he symbolically removed his heart, so he could no longer feel... for his friend Hiro, or for his "love".
Anyone else see that?

