what am i doing wrong

[Masamune·1600]

FFVI uses a 32,768 (2^15) integer variable limit value. While damage caps at 9999, the variable type actually tracks damage beyond the limit. After 32,768, so I understand, the value will reset to 0. It's entirely possible that, could you exceed the damage limit, you would be dealing in the range of 33,000 damage. However, given the game's innate limitations, what should be 9999 damage resets to a minimal value. However, if your magic stat is ≥128, you should be able to deal 9999 damage with much weaker spells.