Your main team must be as strong as possible as they will constantly do damage to boss so balance them well with offense and defense, team 2-4 can go with full offense without any worry. And pray that Nazuna won't meddle or you will waste a precious turn for pitiful damage. Her support is good but it will slimmed your win chance down a lot.

Anyway you don't need to worry whether you win or not. Just whack it when possible to get as many rewards as possible.