Tamakeri is a Japanese term that means "testicle kicking" or, more colloquially, "ball busting." It is a kink as well as a genre of pornography aimed at masochistic men. Tamakeri describes a fetish where men derive arousal and pleasure from testicle abuse, either by looking at pornographic images of testicle abuse or by having their own testicles abused.
The fetish is said to be "prevalent" in Japan, although there are limited sources who cite this. This fetish is most often portrayed by women kicking men in the testicles, which suggests a relation to femdom. However, it has also been suggested that it is the male "kickees" who have the most power in these scenes; by ordering the women to hurt them in the exact way they choose, they are the ones exerting the power in the dynamic.
Some of the information circulating about tamakeri online has been found to be inaccurate or not verifiable. Even so, most sources agree that it exists and that it's a form of BDSM with Japanese provenance.