Girl:

When you first get the Girl fighter, she isn't as strong a fighter as the Boy character and her defense isn't up to the boys defense. But she is still a really good strong fighter. While she doesn't have as much offensive attack magic spells. She is still overpowered as her magic spirits Salamando and Lumina has 3 attack magic spells like Fire Bouquet and Flame Wall and later on Lucent Beam which can also take down boss fights including Dark Lich.

She can also use Cure Water and remedy early on making items like Candy, Chocolate, Royal Jam Obsolete making her the best healer. Also her Dyrad Spell Revivifier makes Cup of Wishes obsolete She can use Analyzer to disarm treasure chest traps and expose boss weakness. Her Lucid Barrier and Wall helps players run away from monsters. I didn't really use Saber spells since they wear out too quickly.

Also you'll want to use Faerie Walnut since she sadly doesn't have the spell Magic Absorb. Also her Defender, Speed Up, Lunar Boost, Moon Energy is very useful especially against the Mana Beast Final boss fight when you have to resort to weapon charging attacks. I also have Girl leading the party along with the Sprite. You'll want spend time to magic grind your spells to a high level since it will make Girl an overpowered wizard and healer character.