I actually didn't use Shion that much. I used her in the last battle just for the 9999 damage attack... well, I probably should have spent more time on her instead of chaos. But that's when I loaded a earlier and played the game again so I could use those "Ancient techniques" for Shion.

The first time I finished the game at like avg level 29, with Kos-Mos being the highest lv 32.