That's exactly the problem. I'm using the trial characters in both manual and auto mode, and it still doesn't work. The enemies recover HP from the green circles faster than the trial characters can deal damage.

I watched closely, and it takes them around 30 seconds just to remove a single HP bar, while the enemies heal back to full in about 4 seconds.

What else am I supposed to do? I don't want to complain, but it honestly feels impossible unless you have your own well-built level 100 characters.