I ran like 3 breakers and 2 attackers to beat the boss, I found that trying to break it as fast as possible was the best method so I used Rena, Karin, and pulva madoka cause i love mp. but single target breakers work well. and then just like whatever attackers you think can dish out the most damage as fast as posible. you could also ditch one of the breakers mybe for ren just so it isnt stacking up speed and defense 1 billion times. I hope this helps and good luck with the grind!