You can reproduce like an anglerfish.

This can work in 2 ways:

If you're male you have to bite a female partner. If you bite your partner long enough they would absorb your body into their skin until only your ballsack remains outside of the place you bit them. The whole process from biting to ballsack takes a few months to complete though you only have to keep biting a few days until the blood vessels and skin in your mouth connects to the blood vessels and skin on where you bit your partner. Once you're a ballsack the only things you could do are sense through your partner's senses and send sperm to their reproductive organs. You can't read their mind but you can feel her hormones so you know what she's feeling. As the rule states though you can reverse this process though it takes the same amount of time to reverse it as to complete it.

If you're female this time you have to be the one bitten by male partners. Again the whole process until your partners transform into ballsacks takes a few months though the time it takes for the skins and blood vessels in their mouths to connect to your skin only takes a few days. You can have as many partners as how much ballsacks can fit into your skin. Like previously your partners can sense through your senses and they also sense your hormones to know your mood but this time you're the one in control whether you want their ballsacks to send sperm to you. You're also the one in control when you want to reverse their ballsackifation.

Btw the kids you give birth to using this power don't inherit the power if you're wondering.

Also yes your ballsack would also be in pain if your partner decides to hurt it. (Unless they inject themselves with anesthesia)