Be aware that playing Challenge mode on a real character can be dangerous on GC and mess up your character data. Techniques above level 15 can revert to level 15 if somebody uses a Disk with that Technique during a stage, thus forcing you to find another Disk in the real game to restore the Technique level you lost (which can be nearly impossible to do if you're a Force and Grants or Megid gets borked, especially).
Your material counter can also reset back to 0, thus allowing you to use extra materials to exceed your normal stat limits, and the only way to fix that bug is to revert to using a memory card backup or to remake your character.
As such, I recommend never playing Challenge with real characters on GC unless you have recent backups, as mules let you get S-Ranks just as easily with none of the risk.