Demon Seed
You've decided to go see a professional witch, to help you be more desirable to women - a bigger cock, more handsome, more raw sexual magnetism, whatever. She's a little bitchy, but you figure it's worth it if you can get what you want. When she finishes her potion, you slurp it down quickly...but soon discover that things may not have been what they seem...your vision blurs, and the witch before you seems...changed...a horned satyr, a dark figure...then back to normal...you try and get your bearings but its no use. The witch has transformed into a cum-hungry succubus, laughing as she explains how she's made you irresistible alright...and right now, she can't resist draining your balls of all your cum! She strokes and sucks and fucks you into three consecutive orgasms, draining you completely until she's finally sated...for now