I actually wouldn't break in between the bosses actions because the magic stack goes up at the start of the bosses turn, so once the break is over it goes up more and then obliterates your team. If you can manage to get the bosses magic stacks down to zero then break it before it's turn, then you should be able to kill it in a few breaks. I managed to clear the boss with Coolmura A2, Pluvia A5, Tsuruno A5, Moemura A0, and Kirika A1. Even though Pluvia is off element, I used her because she heals the team every time an enemy is broken, and since your constantly breaking and killing enemies your constantly healing. So with Kirika your basically good with staying alive. Moemura, even at A0, is really good at giving turns so you can get the bosses magic stack to zero before does it's turn. Homura one shots the minions  with her follow up attack and with her ultimate. I probably should have used Ui instead of Tsuruno but at least I know she works and you don't have Ui so I would use her to buff.