Arahan

In a distant era, a warlord hunts a legendary key believed to grant world-changing power. The pursuit unleashes the dark sides of men as they slaughter one another. The Tao Masters vow not to interfere in mortal battles. Heuk-woon, overwhelmed by rage and power, kills the warlord, claims the key, and becomes Arahan to enforce peace, while the Masters imprison him and guard the key, waiting for the true Arahan.

The remaining Tao Masters bind Heuk-woon in an underground dungeon, using dark Qi to keep him contained. Heuk-woon's hunger for power persists, so the Masters split and guard the key among themselves. They hope that time will bring the day when the true Arahan can restore balance.

The Tao Masters take an oath not to interfere in human wars, preserving the world's fragile balance. Heuk-woon's imprisonment remains in effect, and the key stays hidden among the Masters. The era awaits the emergence of the rightful Arahan who will decide the fate of the key.

Present day begins with Sang-hwan, a clumsy auxiliary police officer, being accidentally struck by an energy attack from Eui-jin during a pursuit. She drags him to her father Ja-woon, guardian of the key, who senses Sang-hwan's extraordinary Qi energy. They decide to train him to become a meaningful protector and possibly end his ridicule.

Ja-woon and the others explain the nature of Sang-hwan's energy and the responsibilities of the key. Seeing potential, Sang-hwan agrees to training, hoping it will earn him respect and stop the taunts of others.

After initial difficulties, Sang-hwan's training yields rapid progress as he learns to harness Qi. He grows more confident and starts to believe he can truly make a difference.

Construction workers uncover an ancient dungeon beneath the city, and Heuk-woon awakens after centuries of confinement. He uses dark Qi to begin a rampage in his search for the key and the power it promises.

Heuk-woon hunts down the remaining Tao Masters and drains their life energy, thinning their ranks one by one. Only Eui-jin's father and Mu-woon stand against him now.

Heuk-woon breaches the Tao school; Eui-jin and Sang-hwan fight back, but the intruder proves unstoppable. Sang-hwan lands a lucky hit with a small boulder, buying them time. Mu-woon pursues the intruder but is killed by a sword thrust.

Ja-woon explains Heuk-woon's past and reveals that the key has been split in halves, entrusted to them. He urges Sang-hwan and Eui-jin to depart with their halves and pursue the threat together.

Eui-jin does not want to abandon her father, and she chooses to proceed while Sang-hwan drives. After a moment of anger, Sang-hwan starts to turn back, but ultimately decides to press on.

The final battle takes place in the city museum. Heuk-woon manages to take both halves of the key from the heroes, but Sang-hwan finally defeats him. The dragon-shaped key seeps into the ground, ending Heuk-woon's menace.

With the danger resolved, the thief from the opening scene is chased by Sang-hwan and Eui-jin as a team. They pursue him together, signaling a new, cooperative dynamic between them.

Sang-hwan's new colleague arrives, and Eui-jin fires the same energy attack on him that started the story. They laugh about their earlier misfires and discuss how to improve their accuracy as a team.

The camera pans up to reveal several people jumping across the city's rooftops, conveying a sense of ongoing energy and motion beyond the immediate conflict.