Stun him at low health then do the QTEs: tap square, X, tap O to unlock this trophy. Athough this QTE puts you in gear 2nd you can do this without 3 bars of meter.
Good luck on this one by the way... he starts only countering after 2/3 life which makes it tough to find an opening to stun him. I lucked out by barely dodging his avalanche attack.
Done during the Water Seven stage. Stun him when he is at low health (Square, Triangle, triangle works well for stunning bosses), then R1 up close when prompted and do the QTEs (X, Right + R2, Spin Left stick) to unlock this trophy.
A seemingly easy full moon boss but keep one thing in mind. If you do not kill BOTH of them on before their turn the other will Samerecarm the other half back to life. Basically you have to fight them all over again. The tank, Chariot and Justice all count as separate enemies so you can debuff them all as shown. The debuffs will wear off after 3 of each enemy's turns.