The wiki states that:
"For a game character, this is a costume other than the standard one that can be unlocked within the game."
However, many game characters, especially in touhou, wear all sorts of differing outfits. And many of them are tagged alternate_costume, such as post #804782, post #805537, and post #797672. Maybe the definition should be refined to say, "Any complete outfit other than the one the character is typically depicted with."
Also, to what extent should we consider a character to be wearing an alternate costume? When they're not wearing much, such as in post #798772, I doubt that should be tagged. Or slight variations, such as post #788759, which I think probably shouldn't either.
Maybe we should have a separate tag for actual existing alternate costumes for a character, and anything else under the blue sky, something else?
Updated by jxh2154