Vampires, Nagas, and/or Driders with biting/blood/pain kink.
When you paid for the naga, you never expected to end up on the other side of her bite. She is a beautiful and very expensive sea snake. Her last owner called her Toshiko. Perhaps it should have been a red flag how quick he was to get rid of her. He even cautioned to keep her leashed in the tank, lest she get out. But she never showed signs of trying to escape, in fact, she was outright pleasant. She was friendly, never talking but always smiling and taking her food without issue.
You made the mistake of letting your guard down.
You brought her her dinner, fresh fish in a bucket. Standing on the ladder, you looked down as she came up to meet you. She took the first fish and you eyed her collar.
"Let me take it off," you motioned her close and undid the buckle. It fell away and for a moment she just looked at you. Then she lunged.
You fell into the water and she coiled her body around you. You thrashed until her fangs sank into your neck, the pain turning into a numbing warmth. You couldn't help but relax in her embrace, her lips kissing where she bit before she began to suck on the skin. Everything was warm and tingly with her. It wasn't unpleasant, even as you began to run out of air.
She must have liked you, though, because she swam back up when she had her fill. She pushed out so you landed on the ground with a thud. A moment later Toshiko followed, slithering from the opened tank to lay over you. Her fingers picked at your clothes as she resumed licking the bloody mess on your neck. The world faded into her touch.
