Battle of Castour Field

The Battle of Castour Field (カスツール平原の戦い) was a minor, yet decisive encounter that took place during the early stages of the Demi-Human War. Occurring approximately 48 years before Natsuki Subaru's arrival in the Kingdom of Lugunica, and two years after the start of the war, a detachment of the Lugunican Royal Army was ambushed and routed by the forces of the Demi-Human Alliance under Valga Cromwell.

Using a small unit of Demi-Human soldiers as bait, Cromwell was able to lure the Lugunican troops onto a field covered in magic circles that when activated tore up the Human battle formations. In the confusion and chaos, the Demi forces were able to advance and surround the enemy. Though the encirclement operation was a flawless success, the Demi-Human Alliance took considerable losses when a lone soldier named Wilhelm Trias broke through the front line, temporarily blunting the surprise attack.

Though both sides took high numbers of casualties, the battle was a victory for rebel forces. A major embarrassment for the Lugunican military, the battle lead to the reorganization of the Royal Army, and the implementation of a new military doctrine with the emphasis on countering magic circles, an idea that would ironically lead to the loss at Aihiya Swamp.

The battle also contributed to the growing reputation of the young Wilhelm Trias, who gained the nickname of "Sword Demon" from a fellow survivor in reference to his actions on the field.

Prelude
In the two years that had passed since the start of the war, and the Demi-humans had proven themselves much more of a threat than previously perceived.

In the prelude to the clash at Castour Field, an earlier battle at Redonas Plateau taking place just days earlier foreshadowed the coming events, where an overextended Human army had been defeated by Demi-Human forces utilizing magic. The battle was the debut of the 15 year old swordsman Wilhelm Trias, who singlehandedly cut through the Demi-Humans cleaning up the remains of the Lugunican army.

As the next military expedition into Castour Field was quickly approaching, the Lugunican military had little time to adjust to the new apparent bait-and-break strategy of the Demi-Human commander Valga Cromwell.

Battle
Days after the indecisive battle at Redonas Plateau, the Humans continued their advance into enemy territory. Suddenly facing a sizable force of rebels in their path, the Royal Army halted their march and immediately began to prepare for battle.

The armies began engaging at sunset, with the renowned Zellgef Squadron, led by the aforementioned Bordeaux Zellgef at the very front. With shock, numbers, and momentum, the Humans slammed directly into the Demi-human troops, completely rupturing the frontline.

Also participating in the battle were several survivors of Redonas Plateau, including Wilhelm Trias and Grimm Fauzen. As Wilhelm typically did, he quickly racked up an impressive number of kills, eighty-eight, including a captain. Facing mounting casualties and overwhelming numbers, the Demi-Humans appeared to rout.

Cromwell's Ambush
Unbeknownst to the Human forces, they had been lured into a massive trap set in place by another Demi-Human Alliance commander, Sphinx. Just as the Lugunican army had appeared victorious, the wide field of magic circles became active. The shaking of the ground quickly threw many soldiers to the ground. The Humans, who had unintentionally walked themselves into a giant magical minefield, began to panic. The whole offensive contingent was immediately made combat ineffective.

Right on cue was the larger Demi-Human counterattack force, who came barreling through the dust and the smoke to surround the disorganized Lugunican army. As usual, Wilhelm Trias committed to his own breakthrough, even as the majority of the soldiers implored him to retreat. Suspecting the genocidal intent of the Demi-Human commander Cromwell, Trias correctly assumed the battle plan of the Demi-Human Alliance, which was to slaughter the retreating Lugunican soldiers after breaking up their front lines with a sudden assault(much like a cavalry charge!).

In defiance of orders, Trias charged into the heart of the Demi-Human assault, and managed to break through with his highly skilled swordplay. Following behind was Grimm Fauzen, who also defied command(with no intent to fight, but rather to retrieve Wilhelm). Despite preaching about how pushing forward into the enemy would be the only way to survive, it soon became clear that Wilhelm's only intent in his "breakthrough" was to get a chance to use his sword. Within minutes, the battle was over.

Soon after, the main force of the Royal Army arrived and rescued what remained of the contingent.

Aftermath
The battle was a major defeat for the Lugunican military, who were forced to reconsider their entire strategy. In accordance with new doctrine, the magical specialist Roswaal J Mathers was brought in to inspect the magic circles. From then on, the military placed magic circle elimination as a priority before entering a battle.

Out of their hundred in their squadron, Wilhelm Trias and Grimm Fauzen were the only two survivors left. Most of the unit formations were wiped out in the initial ambush or were killed in the rout. Fortunately, the Zellgef Squadron took minimal, if any losses. As news of Wilhelm's violent and heroic actions spread around the country, the name of "Sword Demon" became associated with death and blood.

For the Demi-Humans, the battle was a complete success. In the eyes of the Valga Cromwell, the death of so many Humans would bring him pride and inspire him to intensify the war. Conversely, commander Libre Fermi was overall furious at the deadly strategy, and criticized Cromwell's ruthless need to kill Humans. Furthermore, he warned Cromwell that the massive number of casualties would only drive the Humans to escalate the war. In the end, Cromwell only resolved to kill every single Human, and plotted with Sphinx for the upcoming battles.