Removing the tag from all questions effectively deletes it after a day or two.
See also the answer to "How can we get rid of misspelled and unused (or "zombie") tags?":
Tags not associated with any question are pruned every 24 hours on the backend.
Tag counts shown on the tags tab and in the tags autocomplete are also calculated once daily.
"Tristana" seems to be in this case a (playable?) character or character class. While I couldn't find any meta post qualifying if we want such tags, the fact that it's the first instance of such I know of and it isn't needed to find the question (the name is in the title as well) indicates that it can be safely deleted without compromising this site's usability or SEO strategy.