Barbie

Use her early to do campaign mode, upgrading her to 71. Her skills and the fact that early game she is the most powerful fighter, use her in a fighter troop formation maxed at level 71, +5. Doing this will add +25% Fighter ATK and +25% Fighter DEF to your formation.

Once you have Noct unlocked to level 131, +5 he becomes a better hero to use because his troop skills add a +25% HP bonus, in addition to the +25% ATK, and +25% DEF bonus, to your fighter formation that both heroes give.

You should reset her back to 1, and just enhance her to +5 to increase Food Gathering speed +30%.