OMG! This freaking translation... I was aiming at Ending 1, while I successfully get him into the "quell" state, he just keeps spamming healing / shield without fucking again, and the tooltip says I need to get him "calm" (with quotation marks!), and I was just stuck in this infinity loop.
After like 10 minutes of no progression whatsoever, I came back to this thread again, and a quick search tells me this "quell" state is the "calm" state I'm looking for... All I needed was to beat him.
The difficulty of this game leans heavily on the skills you randomly get after every battle, so all you can do is clear every battle on the map and hope for a good set of skills to choose from. Relying on the attack card (red) alone won't get you very far, but those repeatable queues can deal a huge amount of damage, which is the key to victory. On my second run of the game, I was able to get Ending 1 with 0 CV at the end, all thanks to the skills allowing me to just stack "red, yellow, red, yellow, red..." which is so powerful it's almost like cheating.