Battle for the Trias Domain

The Battle for the Trias Domain (トリアス領の戦い) was a minor but impactful engagement that took place in 40 BA, forty years before the arrival of Natsuki Subaru, during the Demi-Human War. The battle marked the turning point of the war as the Sword Saint finally arrived on the battle lines, leading to the war's conclusion a year later later.

Information
The battle had begun as a raid by Demi-Human forces on the lands of the House of Trias, a minor noble house located in Northern Lugunica. The local Human militia was quickly overrun, and the region ravaged, but the Demi-Human force soon met fierce resistance from the "Sword Devil", Wilhelm Trias, who had rapidly arrived from the capital and was himself the namesake of the regional ruling family. Wilhelm, who had joined the battle prematurely and without substantial force was soon outnumbered and overwhelmed by the formidable Demi-Human party, though they themselves were quickly beaten back with the arrival the Sword Saint, backed by the elite Zellgef Squadron of the Royal Army.

Though the demise of the raiding party had little actual effect on the Demi-Human Alliance war effort, the engagement signaled the beginning of the end as the Sword Saint began her campaign to crush the nationwide revolt, which had brought ruin across the kingdom for nearly the last decade. Although the destruction of the Trias lands and the efforts of those who had initially resisted would be quickly forgotten, the arrival of the Sword Saint would go on to become a major event in Lugunica's history.

Background
In 48 BA, long standing ethnic grievances between Lugunica's majority Humans and minority Demi-Humans finally erupted into rebellion, albeit in a leaderless, regional nature. As local lords fought off the growing threats, the Royal Army found itself pressured to crush the revolt. Thus, in 47 BA, a taskforce was mobilized to put down the rebellion, led and utilizing the supposedly overwhelming power of the Sword Saint, Theresia van Astrea. This designation soon turned out to be ill-advised, as the young Sword Saint's pacifist nature, as well as fear held her from participation. The task force was unexpectedly routed, and the group, which included the elder brother of the Sword Saint, was ultimately annihilated in a desperate last stand. From then on, the Sword Saint would refuse to take part in the war; as a result, the war would continue past the turn of the next decade, killing many tens of thousands.

Meanwhile, the role of hero would be designated to individually distinguished units such as the Zellgef Squadron, a unit of elite warriors led by Bordeaux Zellgef who would go on to take part in multiple major engagements, winning great victories as well as suffering major losses. Among those warriors was Wilhelm Trias, who had earned the moniker "Sword Devil" with his lethal swordplay. After defending from a failed assault on the Royal Castle by the Demi-Human Alliance, Wilhelm was himself made a knight. With the Alliance leadership seemingly wiped out, it was expected that the war would soon come to an end. Unfortunately, this would not come to pass.

Contrary to Human strategical views, the momentum of the Demi-Human effort not only failed to decrease, but strengthened and became ever more erratic as the revolutionaries began to lash out in reaction to the martyrdom of their leaders. In the capital city, Roswaal J Mathers arrived to inform Wilhelm of the impending attack on the Trias lands, possibly as revenge for his supposed role in the deaths of Valga Cromwell and Libre Fermi respectively, forcing him to abandon his post and his knighthood in order to defend his home and family. In that, Wilhelm was unknowingly inspired by a brief conversation with the Sword Saint herself.

Arrival of Wilhelm Trias
By the time Wilhelm had arrived at the Trias Estate, rebel forces had long since infiltrated and sacked the region. Lacking strength in numbers, ability, and in mind, the House of Trias and its vassals immediately fell to the Demi-Human onslaught.

Alone and without any kind of support whatsoever, Wilhelm was immediately surrounded and brought down by Demi-Human warriors. At that moment, as he lay on the ground wounded, it would seem as if fate, among his impulsive nature and all his battlefield sins, had finally caught up to him.

Arrival of the Sword Saint
With the force of a typhoon of steel, Theresia van Astrea burst onto the battlefield, dancing about with grace as she sliced through the ranks of Demi-Human soldiers, and with such speed that many of the soldiers could not even recognize that they'd been cut in half.

The Zellgef Squadron soon arrived, though they would not be reinforcing the Sword Saint, not as if assistance was needed. Wilhelm was rescued by Bordeaux Zellgef and Grimm Fauzen, while Theresia continued to wipe out the Demi-Human force in the area without much effort. The Kingdom of Lugunica had finally brought its greatest weapon to bear.

Aftermath
With her stellar performance on the battlefield, the Sword Saint had dispelled every doubt or rumor concerning her abilities. Though over three hundred troops had been killed by Wilhelm, only the nearly one thousand slain by Theresia would be remembered. Her first defeat earlier in the war was erased from memory and forgotten, and the Battle for the Trias Domain would forever be remembered as her only debut in battle. And thus, the Sword Saint would from then on lead Lugunica's war effort, breaking down the Demi-Human's will to fight through sheer power and brutality. Only months later in 39 BA, King Gionis Lugunica would meet with the Demi-Human representative, Cragrell Dawson, for peace talks. The Demi-Human War came to an end after nine years.

The Trias family would cease to exist, with Wilhelm Trias being the sole surviving member. Wilhelm, in shame, anger, and regret would soon disappear from the army after facing the Sword Saint one last time in the aftermath of the battle. The legend of the Sword Devil would be forgotten, with its place being taken by the actions of the Sword Saint. He would not be seen again for another two years.