Yuusha Battle System
It seems the safest way is to repeatedly hit them with fast attacks such as the default top one. Spamming that move worked well except against the large amazon who uses blue (magic?) attacks often. Having a full green bar allows you to block red (physical?) attacks and since short moves such as default top take so little green (stamina?) it regens quickly to block the physical spamming heroines.
For those who have trouble winning the fights, there's a cheap little trick:
Just wait for them to attack you with a hp attack and do nothing. You will most likely block the attack. Then counter with a fast hp attack (red triangle button). Most of the time, the girl will then attack you again with an attack that you can dodge if you do nothing. Repeat. Win. Be liked by Sefi. Win again.
Works 90% of the time.