Also known as War of the Arrows, the film takes place during the Second Manchu Invasion of Korea, in the 1630s. Nam-Yi and Ja-In are brother and sister in Korea, adopted by the ruler of a northern locality in Korea after their father is killed for treason (likely being loyal to the previous regime).
Fast-forward several years, where both siblings have grown up. Both have trained as skilled archers, with Nam-Yi a true master of the martial art. His trademark skill is the ability to curve the path of the arrow around obstacles to hit targets at seemingly impossible angles. During Ja-In's wedding to the local ruler's son Seo-Goon, Manchurians invade the village, slaughtering many of the villagers (including Nam-Yi's and Ja-In's adoptive parents) and taking the rest as prisoners of war (including Ja-In and her new husband). Nam-Yi wages a one-man guerrilla war against the invaders, seeking to retrieve his sister and bring her back home to Korea.
Arrow: The Ultimate Weapon provides examples of:
- A Father to His Men: Jyuushinta is an antagonistic example.
- Aloof Archer: Nam-Yi, while something of a goofy slacker in peacetime, becomes a calculating, precise sniper once the Manchu soldiers invade.
- Annoying Arrows: Generally averted. Most characters shot by arrows who don't die immediately are severely hobbled or crippled by their wounds. Nam-Yi plays this straight a couple of times, but that's because he's The Determinator (see below). Some types of Manchu arrows also seem to overpenetrate, repeatedly going clean through a victim without killing them on the spot.
- Artistic License – History: The attack dogs used by the Manchu in the film's opening scene look like German Shepherds, a breed that, aside from being geographically misplaced, only came into existence toward the end of the 19th century.
- Badass Army: The Manchus. Upon their introduction, they slaughter the town's Joseon army garrison before the latter could land a single hit. For all their Rape, Pillage, and Burn routine and occasional missteps, they carry out their pursuit of the heroes with remarkable competence and daring, and repeatedly have them on the ropes by using group hunting tactics to surround and pin them down.
- Bad Vibrations: When the mounted Manchu army is inbound, Nam-Yi is the first to realize it when he sees one of his arrows, stuck in a tree trunk, vibrating. As the army approaches, the vibrations get stronger and start rattling teacups in the village.
- Berserk Button: Threaten to do any harm to Ja-In, and Nam-Yi and Seo-Goon will see that you barely live to regret it.
- Big Damn Heroes: Done at least twice: Once by Nam-Yi, severing a bowstring and allowing Seo-Goon to charge and kill an enemy officer, and once by a tiger that saves Nam-Yi from Jyuushinta and his troops.
- Bows and Errors: The protagonist is an archer who can curve his arrows in flight. He does this by twisting the bowstring around the arrow before firing. This would absolutely not work in real life.
- Camera Abuse: Possibly unintentional. In the scene at the river crossing, there are obvious droplets of water on the lens of the camera in certain shots.
- Chekhov's Gun: Early in the film, Nam-Yi's friends stumble upon a tiger's den while hunting, and wisely decide to retreat immediately. Later, Nam-Yi lures the pursuing Manchu soldiers to the same spot, causing the tiger to attack and kill several of them.
- Chekhov's Skill: Nam-Yi's ability to curve arrows around obstacles. To a lesser extent, his ability to make and use a Korean short draw device (used to fire arrows shorter than the draw length of the bow).
- Combat Pragmatist: Nam-Yi relies on stealth, times his attacks patiently, and resorts to an assortment of very underhanded tactics to outmanoeuvre the bad guys throughout the film.
- Colour-Coded for Your Convenience: In-Universe, the Manchurian commander knows that the same man (Nam-Yi) is behind the attacks on his soldiers because of the red-fletched arrows he shoots. Also serves a symbolic purpose, as many of the white-fletched Manchu arrows that Nam-Yi scavenges and uses become red from passing through a body.
- Conservation of Ninjutsu: At the start of the film, Nam-Yi hits every target he aims for. As the number of Manchu he's facing diminishes, their accuracy improves while his starts to slip.
- Crouching Moron, Hidden Badass: Gang-Du and Gap-Yeong, Nam-Yi's goofy hunting buddies, are surprisingly good fighters despite their role as comic relief.
- The Determinator: Nam-Yi and, to a lesser extent, Seo-Goon are both wounded at one point or another in their dominant arms (Nam-Yi in his drawing arm, Seo-Goon in his sword arm), yet lose very little of their deadliness for it.
- Defiant Captive: Ja-In remains resolute, calm, and defiant whether under threat of rape or while being starved. And then after she is given food, declares that she only took it to replenish her strength and attacks her captor with the skewer.
- Evil Cannot Comprehend Good: Nam-Yi hesitates to kill Jyuushinta, the Manchurian commander and Big Bad, because Jyuushinta is trying to keep one of his wounded men from falling down a cliff. When Jyuushinta confronts him about it later, he accuses Nam-Yi of doing so out of contempt.
- Heroic Sacrifice: Nam-Yi's two hunting companions sacrifice themselves once one of them is injured, to delay the Manchu. At the end, Nam-Yi pulls an arrow out of his heart, knowing that he will die, in order to use the arrow to kill Jyuushinta.
- Improbable Aiming Skills: Nam-Yi's ability to bend the trajectory of his arrows is unbelievably useful and unbelievably unbelievable.
- Karmic Death: The Manchu prince routinely rapes one of the female prisoners every night on the army's way back to Manchu. When Ja-In resists, he attempts to break her. His unwillingness to accept help from his soldiers when struggling with her allows Nam-Yi to sneak up on him, leading to his eventual assassination.
- Master Archer: Nam-Yi, Ja-In and Jyuushinta are all superb archers, with Nam-Yi being finest.
- No "Arc" in "Archery": Played with. Most of the archers appear to aim at realistic angles for the targets at which they're aiming, but there are a few shots of bows aimed almost directly at faraway targets, and of arrows in flight suffering minimal drop.
- One-Man Army: Nam-Yi is a more realistic example of this trope. It's his speed, aim and intelligence that allows him to silently murder scores of Manchurian soldiers, not superhuman strength or endurance.
- Panthera Awesome: Nam-Yi manages to provoke a tiger into attacking the Manchus.
- Pre-Asskicking One-Liner: Ja-In says one, right before charging the Manchu prince with a skewer.Ja-In: I am a warrior's daughter. I shall not beg for my life, nor shall I die in vain.
- Rank Scales with Asskicking: Min-Soon, Nam-Yi's and Ja-In's adoptive father, takes up a sword to defend his village, killing multiple soldiers before being killed. Seo-Goon, his son, does even better, helping to free the village captives and rescue Ja-In.
- Those Two Guys: Kang-Du and Gap-Yong, Nam-Yi's hunting buddies. They help Nam-Yi and Seo-Goon on their incursion into Manchu territory.
- Trick Arrow: Minor example. Nam-Yi at one point uses a short arrow while hunting, as well as to hobble one of the Manchu soldiers pursuing him. In real life, these shorter arrows were apparently used by snipers to prevent the arrows from being used by the enemy.
- Villainous Valor: The Manchus. The latter parts of the movie is largely shown from Jyuushinta and his men's perspective, allowing us to see their sheer relentlessness in full. They use squad tactics to try and get the drop on Nam-Yi, back each other up on dangerous situations readily, and maintain near-perfect discipline despite being visibly shaken by their casualties. The movie makes a point on showing how they look after each other, since the Manchus were strategically outnumbered in real life and relied on Chinese/Mongol auxiliaries to bolster their ranks.
- Vomit Indiscretion Shot: Nam Yi vomits all over Seo-Goon's face during their drunken brawl early in the film.
- You Have Failed Me: Unspoken example. After Jyuushinta and his soldiers find out that the prince was assassinated, one of Jyuushinta's soldiers kills the guard in charge.
- You Shall Not Pass!: When many of the prisoners are being chased down and slaughtered at the Korea-Manchuria river crossing, Seo-Goon steps up to try and prevent any more soldiers from attacking the fleeing prisoners. He succeeds, in badass fashion.
- Zerg Rush: Done to the Manchu troops at the river crossing by the captured prisoners. When the Manchu prince congratulates his uncle for capturing more prisoners than they have soldiers, this was pretty much inevitable.
