I wanna go with FFVI here. Some of the game is very Steam Punk but the technology level more or less is about where FFIX was. The characters are also unique, each stand out in a similar to how the cast did in that game. The story is very dark at times but the aesthetics do pull off some of the whimsical feeling of FFIX. You don't get to master abilities and passives but the system is slightly similar in that A LOT of equippable items do give you abilities and passives, you just can't learn them permanently. It's a great game that you should nevertheless play if you haven't already.

They are very different games but you may nonetheless want to try Final Fantasy Tactics. A lot of the two games' customization systems share similarities, partially because a lot of the FFT developers moved directly onto FFIX after finishing the game, whereas the FFVII team stuck together to make FFVIII and FFX.