Slaying monsters for the feeble

"I'm bound to a demon. For my entire life, I avoided magic at all costs. Now, I'm responsible for a demon who wields magic more powerful than the toughest mage or sorcerer. Demons are evil. That's what my textbooks say. That's what I see. He's ruthless; he's temperamental; he's cold. But he protects me without fail. I wonder if he's hiding a heart behind his hostility. My demon is a monster. Whether he's heartless or not, my contract with him is...