War in Prison World 2
Souta ordered the rebel army to retreat when he found that the empire's forces were heading in their direction. His shadows collided with them, and the shadows managed to eliminate some of the forces, but there were too many of them, and the shadows were crushed.
Even though they could regenerate by using Souta's best feram, they were still crushed, so Souta decided to disperse them. It was consuming his energy after all, and energy was important to release his full strength in a battle.
At the very least, they've managed to eliminate a large portion of the empire's army that was on this planet. It was enough for them.
The rebel army retreated to their base and fortified their defenses. They knew that they infuriated the empire, and the empire would attack them.