agree with @Jor25. there are a couple of other things as well that I would change.
1) mention humiliation. I think this is a clear example of a masochist, but there isn't really any depiction of pain (tw loli) pg60 #167586|Kodomo Datte H Nano | They're just kids…|58,067
2) remove "someone else." You can harm yourself and still enjoy the pain
3) remove "dominate"." This reads like [submissive] which is its own separate tag, nor a necessary description of it
I stole this from Wikipedia: "someone who derives pleasure from receiving physical/mental pain, or humiliation. Also known as sadomasocism, or S&M"
Might be helpful to append a bit onto the description that having one character call another character a masochist isn’t enough to count. The word gets used a lot as part of degrading dirty talk.
Agreed with Dziun. No tag involving/implying pain or discomfort has a reliable way to filter out non-con or otherwise unwilling depictions of pain, whereas tags such as "rape", on the inverse, help narrow in on these things. I know at least I would prefer a tag that would filter these out, and allow the masochistic stories to be more easily accessible without a convoluted list of tags and -tags in my search bar.
This tag is hugely needed, as there is currently no way to find works where characters are willingly seeking out pleasure from pain. BDSM and other such tags cover too much fetishes too be usefull for this purpose.