Attack boost
After reaching Undelwalt and going to the seventh path through the sixth, defeat the Idols in the Dark Forest. Go the union and get the reward for defeating Idols (Comet formation). Use that formation with your best leaders. This can result in your leaders doing 15,000 to 54,000 damage each combat or Mystic Art, and 60,000 to 240,000 for Weapon Arts.