To explain it in more detail, it comes from the manual from the 9th Touhou game, Phantasmagoria of Flower View. It's a bit different then other Touhou games, being a two player competitive game. The page of the manual was labeled as is most manuals explaining HUD elements.
Crino was the second player in the screenshot and was labeled "9"
In the descriptions of what each labeled thing was, 9 was simply "idiot."