Chapter 1: The Vengeful Dancer
Leda cannot handle healing, and a high critical rate does not guarantee a kill. Keep Buccar ready to finish, then advance toward any enemies that refuse to approach.
Leda starts with a Bronze Sword and Bronze Bow. Blindside has only a 5% chance to prevent counters, so plan attacks assuming she will be countered. 
Sirocco restores 5 HP to himself after combat. Leda cannot heal yet, so do not save her action as a healing backup. If you want to save Leda's levels until after changing class, hold off on singing at the start and give 
Mu as much kill EXP as possible. Keep 
Buccar ready to finish enemies. Even a high-critical combat art can fail to kill. Advance if the remaining enemies refuse to approach.
Delay Leda's levels until after changing class
If you plan to save Leda's levels until after changing class, do not use Song of Passion at the start. Give finishing EXP to Mu, who has Signs of Growth, whenever possible.
When Leda initiates, Blindside has only a 5% chance to prevent a counterattack. Calculate incoming damage as though she will be countered before attacking with either the Bronze Sword or Bronze Bow.
Sirocco restores 5 HP after combat
Sirocco's Goddess's Favor restores 5 HP to himself after combat, including when he is attacked. Include those 5 HP when calculating his remaining health after an engagement. Leda cannot heal allies yet, so arrange recovery separately.
Keep Buccar ready for the finishing blow
When trying to kill with a high-critical combat art, save Buccar's action to finish the target if the attack does not crit.
Advance if the remaining enemies do not approach on their own.
Equip Sirocco with a Catalyst for another caster
This route has few mages. Give Sirocco a Catalyst to add another spellcaster.
Leda
Buccar
Sirocco
Mu