The Power of Hate. (Hate is the Strongest Force in the Universe.) The hero's overwhelming hatred for the villain and all the horrible things he's done sees him through all his trials just so he can take that son of a bitch down hard.
The hero makes a stirring speech about how his love will prevail over all, but when it gets to the fight, the villain beats him handily. As the hero lies dying on the floor, the Mooks lead his love away to be executed.
"The Power of Love" is revealed to be something more mundane such as simple extreme devotion towards a goal or person. Other emotions, such as hatred, would grant the same magnitude of power (if not more-so as it is easier to hate than love).
Asexual (well technically aromantic) characters are incapable of tapping into the power (for obvious reasons) and find themselves inferior to those who can actually have love in their hearts.