So lets go over special character mechanics...
Aya - to be decided, perhaps a white mage monk mix or maybe just white mage. Will get back to everyone on that.
PB - The party tank, deals pretty good physical damage too. PB's abilities tend to raise enmity forcing enemies to target him over other members. His key powers are Provoke, and Aegis. Provoke causes enemies to target him over other party members (minus multi hitting skills), while Aegis causes his HP, Defense and magic defense as well as making him immune to status effects for the five turns Aegis lasts-however it prevents him from making any actions. Mixing Provoke and Aegis allows him to tank the enemy parties for a time. Other wise PB will have some damaging physical skills and "Charm" that cause an enemy to attack it's allies for a time.
Sakura - The main magic damage dealer of the party, Sakura has moderate physical stats too; she can cast sword spells that inflict elemental damage on single or multiple targets. She can also infuse her weapon with elemental magic that allows her physical attacks to deal further damage. Sakura's unique mechanic is "Aether Flow" and Aether Dam", using Aether flow doubles her magic damage but also her MP costs, while Aether Dam halves her magic damage and MP cost as well as granting her a hefty MP regen for as long as the Aether Dam stance is kept active. Swapping between the two stances permit Sakura to remain at full MP at all times while maximizing her damage.
Phi - The speedy rogue of the party, she has high agility, luck, critical, and evasion. Phi can't take hits well but by using her various powers she can evade damage all together, lower the chance enemies will target her or increase her ability to crit making her a very powerful physical attacker. Phi's high luck means she'll grant the party higher drop rates, her unique mechanic is the ability to steal enemy stats for a few turns debuffing them and gain a buff to her own stats. Her abilities mostly deal with status effects otherwise.