Years after the threat was eliminated and Yuuto had regained the support of his people, a new challenge presented itself to the kingdom. A neighboring kingdom had begun to encroach on Yuuto's territory, attempting to expand their domain. At first, Yuuto tried to resolve the issue through diplomacy, but the neighboring king refused to listen, stating that his kingdom was weak and ripe for the picking.
Despite the diplomatic failure, Yuuto still hoped to avoid the conflict. He knew the cost of war and the toll it would take on his people. However, when he discovered that the neighboring king had already gathered a formidable army to invade his territory, he knew that his options were running out.
Yuuto authorized a defense which involved a combination of defensive corridors to stifle the attack and fortified positions to hold and outlast the invaders. With the fortification complete, Yuuto hoped that the invading army would be discouraged, thinking twice about making any further attacks.
But that was not to be. The neighboring kingdom attacked with a great ferocity, resulting in a brutal and bloody battle. Despite the district lines' fortification, Yuuto's army was outnumbered three to one, and the battle was quickly turning against them.
Yuuto recognised the need to stop the invasion, so he made a courageous but risky decision. He authorized his mages to use forbidden magic, which would unleash an uncontrollable and devastating force capable of destroying the invading army in one fell swoop.
The mages, at the cost of their own lives, cast the spell, and a massive wave of unholy energy ripped through the battlefield, shattering the invading army and causing significant damage. The neighboring king's army was decimated, and the surviving soldiers were left in a weakened state, incapable of retaliating.
Yuuto had successfully nipped the invasion in the bud, but the cost he paid was immeasurable. The use of forbidden magic had forever stained his name, disgracing him, and generating fear in his people. Moreover, it was not just the stigma of the forbidden magic that was costing him, but the innocent lives lost and the number of injured, afflicted with unwarranted suffering.
The people of Yuuto's kingdom were outraged that he had made such a drastic and costly decision, crossing the ultimate line that had been taboo for centuries. They had believed that their kingdom was better than that, better than using such magic for any reason.
Yuuto realized his mistake immediately, apologizing and begging for his citizens' forgiveness. Yet, it was not enough. The people had lost faith in their leader, accusing him of exploiting the forbidden magic for his own selfish gain rather than for the greater good. Some even called for him to relinquish his reign, claiming he was a menace who had become drunk on power.
Yuuto understood their reasoning and deeply regretted his actions. He had crossed the line that he himself had drawn, ignoring the cost of the very gift he used, tearing down the morals he had believed. He realized that the villagers that once praised him had been completely right, for it was his winning strategy that lost their trust.
In the end, Yuuto's use of forbidden magic was a turning point in his reign that he realized he would never forget. He knew that the damage done could not be undone, and that he would forever carry it as a reminder of the cost of power. Still, he persevered, learning from his mistakes and doing everything he could to redeem himself in the eyes of the people he served.