He could feel a laugh bubbling up in his throat. Cruelty in every timbre of the noise if he let it fall from his lips, that ongoing amusement at poor Prompto’s expense not something he had tried to hide. And though he did not laugh, not this time, it shone behind his eyes.

“Don’t give me that look.” Like an animal freezing up, fight or flight instincts stalling in the face of futility. “You’d only be fulfilling what you were created to do. To be. Maybe more than that; my blood might even be potent enough to twist you into something truly special.”

There was no 'might' about it. He knew that was the case.

"It'll hurt, just a little. But it wouldn't be terribly fun otherwise."