The pain was almost as intoxicating to Zira as the pleasure. He enjoyed it. He'd never realised he had such masochistic tendencies before, but now that he had discovered that little fact, he drank it up. He felt more aroused when his cock was bound, erection denied. It made his appreciate the real pleasure more, and appreciate the moments when Crowley freed him from the binding confines of the rings.
"Freed as he was now, he felt exposed and vulnerable, which was erotic in its own right. The vulnerability to Crowley was exciting, with his throbbing cock hanging between his thighs. Though the device was removed, he wouldn't touch himself unless given permission to do so, lest Crowley put him back in the Gates without the fucking he'd been promised.
"May I pleasure you, dearest?" He hadn't been permitted to fuck Crowley for weeks. His cock swelled noticeably at the thought of burying his flesh in the demon.