FF2J was the NES version, featuring no improvements on spells (ie: fire, fira, firaga) but instead a improvement-by-use, where after you use a skill # times, it levels up, increasing in effectiveness depending on what kind of skill it is (fire will improve damage-wise, sleep will improve success-wise).
Its actually a really interesting system, though it could be taken advantage of by running around in the first area spamming spells and powerleveling your skills/stats, lol.
--J