In the Kingdom of En-Land, Crown Prince Heeseung, a stoic and strategic leader, watches with growing concern as neighboring Areon suffers relentless attacks by thugs from the northern outlands. As a gesture of alliance and leadership, Heeseung steps in to lead the war effort and announces a royal decree: every able man from every household must join the war.

In Areon, Ara, the fiercely intelligent and graceful daughter of the district's ailing lord, is devastated. Her father, once a great commander, lies bedridden, and with no brothers to represent their family, she sees no choice but to take action. Disguising herself as a boy, she cuts her long hair, dons her late brother's armor, and slips into the army under the name "Aren."

As the war progresses, Ara (as Aren) proves to be a capable and fearless soldier, catching the eye of Prince Heeseung. The two begin to form a bond — one built on respect, loyalty, and silent admiration.

But secrets don’t stay buried for long. When Heeseung stumbles upon the truth of Aren's identity, he's torn — between duty and emotion, between tradition and the undeniable pull of his heart. He feels betrayed, yet deeply moved by her bravery.

As the final battle looms, the kingdom's fate — and their hearts — hang in the balance. Will Heeseung expose Ara’s secret, risking her execution? Will he deny his feelings to protect his crown? Or will love rewrite the rules of war and royalty?