Ordinary fui has first appeared in IWGH. It is listed in the game as fui, and is later unhelpfully defined as “just your ordinary fui”. Further in the game, a veil on the mystery is slightly lifted:

Fui do not come in large quantities and thus a fui should be valued and not disposed of lightly. Fui sellers are far between and never stay in one place for a long time.

The game also says that fui grow on trees. Scholars believe this might be bullshit.