You must defeat Yumisu in a turn-based battle.
As the Demon Queen's power grew, so did her ambition. She sought to conquer and enslave all the realms, forcing their inhabitants to bow to her will. Her armies of dark creatures marched across the land, leaving destruction and despair in their wake. The people lived in constant fear, wondering if they would be the next to fall under her evil grasp.
Save your burst cooldowns for the second Dread Knight wave. The first wave is a decoy—she casts “Mockery” if you blow everything too early.