Thanks for the suggestion but I won't add any more predefined categories at the moment, the constant recreation of the ones in existance is already taking up a lot of resources on the server. But the main reason is that those two categories aren't very reliable, many quality story flashes are not categorized as such and would then be missed by people if they went directly to a possible combined story/clean/quality/thebest subsection.
You can always do a CTRL+F search for "quality" or "the best" on the story/clean pages, though I understand if it feels tedious. Someday I will make a category selector which will make it possible to puzzle together your own custom categories.
