Futa.

Walking into the futa's home your excited to finally get your cage off. "I left the key in my bedroom, just follow me" not suspecting anything you follow the futa to her room. "go ahead and take a seat on the bed. I put the key somewhere but that was like a month ago so it might take me a minute to find it. would you like a drink or something?"

Sure I'd love something to drink. The futa hands you a soda "here you go sissy" being parched you gulp it down all at once. After a few minutes of waiting you feel funny. Your dick was trying to grow in it's cage uncontrollably and it's painful. What the hell did you do to my drink!?!

"There was a Viagra mixed into it, haha, now your going to submit to me or your going to be stuck in pain for hours as your dick tries to grow in it's cage."

Not being accustomed to pain whatsoever you immediately surrender to the futa. Fine I'll do whatever you want once you take off the cage.

"Then we have a deal."