AO3 Primary Ship Search v1.0
This add-on adds a checkbox to AO3's search page that will make the search exclude results where the ship tag isn't the first relationship tag listed. This helps cases where the search page is flooded with stories about other ships, where your ship is present and tagged, but not in focus.
Because of how AO3 renders its search pages, we can't grab more search results to replace the dropped ones, so this means fewer search results per page. It's possible you could even get a totally empty page of search results, although I haven't seen this happen in the wild.
If you search with multiple ship tags, the search will include any story that has any of your listed ship tags as the first tag.
Obviously this doesn't guarantee that every story will feature your ship as a focus; but in general, people tend to put their fic's primary ship first and then add secondary ones later, so it's a pretty good heuristic.