"Of course, pet." He set the knife aside for the moment, dropping to his knees in front of her. Arms shackled above her, legs spread open for him, she was completely available. It was perfect. A third finger joining the first two, gently, his tongue began to lap at the outside of her lips around his fingers. As her breathing sped up even further, he moved higher, flicking the tip against her clit lightly. She groaned and whimpered, and he wrapped his lips around her button, his three fingers increasing their pace and curling inside her, his tongue moving more and more rapidly. He let his teeth just barely graze her clit, and it was almost more than she could bear. A few more strokes of his tongue and thrusts in her pussy and she came loudly, moaning and bucking slightly against the wall. He kept moving quickly to her peak, then slowed down his fingers and tongue as she came down, gently letting her relax with just the slightest brush of his tongue against her pussy to lengthen her pleasure. Her body slumped somewhat against the wall, head hung again, having released some tension with the orgasm.
He reached up and undid the shackles gently, wrapping his arms around her waist to steady her. It probably wasn't such an intense orgasm that she needed it, but when the knife came into play he was never sure just how powerful they were. She relaxed against him for a moment, mouth blindly kissing his neck and shoulder, hands stroking down his back. "Thank you, sir. That was wonderful."
"Did you think I'm already done?" He asked, smirking. Leaving the blindfold on, he led her over to the bed, helping her onto it. "All fours, pet." She complied, curious what would happen next, but hopeful and excited.
Her hopes were confirmed when she felt the coldness of the knife again, now trailing down her spine ever so carefully. His free hand rested on her hip, his eyes hungrily devouring the view in front of him. He never tired of her ass presented to him in such a wonderful way. As the knife reached her lower back, he removed it, placing it against her skin just under the shoulder blade
Even under the blindfold, her eyes closed in pleasure as the second cut began. A little deeper, it refueled the fire between her legs that had been momentarily sated. Soon she was arching herself even more, body language begging him to take her, even if she stayed silent for the moment (other than the occasional moan, sigh, or happy whimper, of course.)
Despite his earlier orgasm, he had been rock hard almost the entire time, and was more than happy to take advantage of what was offered to him. Positioning himself behind her, he carefully set the knife aside and grabbed her hips, pushing his length into her fully, but not harshly. Leaning over her, he lapped at the pooling blood on her back as his hips slid back and forth slowly, warming up. She moaned quietly under the attention, though her noises quickly became louder as he pulled away from the blood, increasing his pace inside her. Reaching under his pet, he cruelly tweaked one nipple, cock moving faster and faster until the skin smacking on skin was audible. She moaned, sighed and cried out under him, doing her best to push back against him, moving steadily towards another orgasm. The added sensation from his attention to her breast, and then the same hand moving to strum a finger against her clit as he fucked her, only drove her higher and faster. He, of course, was right there with her.
Finally, she came first, screaming out and stopping all motion, though her entire body shook with pleasure. Her pussy clenched so tight he was forced to stop moving, his cock deep inside her as her orgasm set off his own. He groaned and shut his eyes, pumping deep inside her as she spasmed around him. They came down slowly, he leaning over her back as both sets of muscles relaxed, lightly kissing her shoulder blade, shoulder, and neck. After a few moments he slowly pulled out of her, letting her collapse onto the bed before lying next to her. She let out a contented sigh, head half in the pillow, as he leaned over to take one last lick from the cut on her back. "Thank you, sir. It was a wonderful birthday present."