The usable styles are determined by the handedness of the weapon, which in turn depends on Race and Weapon Size. The table below shows what weapon sizes each race can equip, and the basic wield style they will have with a weapon of that size. One-handed means it takes one hand to use the weapon, Power Grip means it takes both hands to use it.
|Qsiti||One-Handed||Power Grip||can't equip||can't equip|
|Mitra||can't equip||One-Handed||Power Grip||can't equip|
|Yama||can't equip||can't equip||One-Handed||Power Grip|
|Sovani||can't equip||Quad Wield||Dual Power Grip||can't equip|
Since Sovani can't single-wield, their styles are changed to Quad Wield for one-handed weapons, and Dual Power Grip for two-handed ones. The only true Two-Handed weapons are Spears and Staves (polearms), equipping these will change the wield style to Two-Handed, or for Sovani, Dual Two-Handed.
Using a one-handed weapon opens up further possibilities. All one-handed weapons can be wielded with two hands in Power Grip style, you can even change styles in the middle of a battle to use Power Grip combat arts. In order to do this however you must have at least one Power Grip combat art learned. This works even if you have a shield equipped in your off hand, although putting the shield away obviously negates its defensive benefits.
The other option is to equip another one-handed weapon in the offhand, this turns the wield style into Dual Wield. Dual Wielding has the further advantage of being able to put the second weapon away during combat to use either One-Handed or Power Grip combat arts (if you know any). Although this may seem very appealing, please note that this significantly slows down the development of these wield styles, as the game engine will mix all the usable arts into the Battle Commands. Luckily this problem has been solved for the PC version, where you can disable the arts you don't want your characters to use. Weapons of different types can be dual-wielded as well, but in this case only the arts available with the main hand weapon will be usable.
It is also worth noting that most (if not all) Weapon Arts can only be learned with the basic wield style of a weapon, which means that to learn any Weapon Art with a one-handed weapon you must develop the One-Handed style.