A burning temple. A young boy and a monk frantically escapes from the fiery blaze until the latter stops at one point to hand Kotarou, as the lad is known, a valuable object and asks that he sell it for money and in turn seek refuge at another temple, where a monk by the name of Zekkai will take him in.
Elsewhere, a bandit scout spots an convoy lead by two local Japanese men from afar, as he quickly returns to base to alert his oyabun. The bandits head out to seek out their prey, and manages to ambush their victims. One of the escorts is killed an arrow, and what follows suit is a barrage that rains upon the seemingly helpless convoy. Speaking in an foreign dialect, the convoy leader tells his men to protect the cargo that they are bringing. With the crates secured, a lone bodyguard uses the dead escort as a meat shield to fend off against the flurry of arrows, as he charges head on towards the attackers. He succeeds in taking out the entire group of bandits as quickly as he had approached them. Leaving only the oyabun, the bodyguard taunts him by challenging him unarmed, incurring the wrath of the katana wielding bandit leader. Swinging his weapon about in rage, the bandit leader misses all his strikes and is dealt with a swift deathblow by the bodyguard. As the dust settles, the bodyguard laments in Chinese on how pathetic the swordsmen in Japan were. Revealed is the face of a Caucasian male.
In a fishing village faraway, Kotarou teams up with his loyal pet dog to distract a villager as he enters his victim's home to steal provisions. Proud of the spoils they had obtained for the day, Kotarou and Tobimaru head back to their hideout, which is an abandoned shrine at the top of the hill. Unknowingly, Kotarou finds a suspicous person inside, and after failed attempt to drive him out, he merely ignores the drifter. While cooking the fish he had taken from the fisherman, the boy is surrounded by two army personnel who is accompanied by an unknown person. As they violently try to seize Koutaro, the drifter suddenly finds himself an unwilling participant in a fight. With the two soldiers down, the third attacker reveals a metal whip and proceeds to take the drifter down, who is caught off guard when a kunai suddenly flies towards him. Fortunately, Tobimaru intercepts the flying projectile but is hurt in the process. Regaining momentum, the drifter finishes off his opponent with a hard thrust to the throat with the hilt of his sword. Just as he was about to leave, Koutaro pleads with him to save Tobimaru's live and offers the valuable object he had received earlier from the monk in exchange for safe passage to Shitaro. With nothing to lose, the drifter agrees to the deal.
Meanwhile, a local daimyo grows suspicious at why the Chinese convoy is rushing with the construction of the structure they had commissioned, paying a handsome sum for its completion too, as he wonders if it had anything to do with the capture of the boy they were after... After a long horseback ride, the drifter and Koutaro manage to seek the aid of a doctor who temporarily manages to heal Tobimaru though the path recovery seems certain. Back at the shrine, the daimyo's men and a lone Chinese convoy member find their brethren killed although they have no idea who the culprit is. For some unknown reason, the men then surround the Chinese in an attempt to subdue him. We return to the drifter, whose name is still unmentioned as he heads to the local village after a long night's rest, where he learns of Rarou, the sole caucasion from the Chinese convoy. As fate would have it, their paths cross, with the ever battle hungry Rarou provoking the drifter, as an inevitable fight ensues. Unfortunately it comes to a premature end when Rarou is informed of the deaths of his subordinates.
The drifter returns to a prejudiced Koutaro who accuses the latter of trying to sell him out, despite being provided with a proper reason. The tension is interrupted by Tobimaru's sudden awakening, with the drifter handing Koutaro some medicine to help flush the poison away. In a meeting room with his superior, Rarou provides a full status report on the circumstances of the two dead Chinese envoy members, with one being kept alive after having his death faked by the daimyo's men. After waking up from a nightmare, the drifter is asked by Koutaro on the charm placed around the hilt of the sword that prevents him from drawing his sword, though the latter refuses to provide a straightforward reply. The conversation then turns into a light hearted one, as Koutaro questions the drifter on why he treats horses so well, to which he responds by saying that riding a horse on full speed provides the same euphoria that flying does. Like the curious little boy that he is, Koutaro hitches a ride on the horse once again in attempts to handle the beast himself, faltering in the process. A wanted notice is out, and the daimyo seeks for Koutaro's capture. All efforts by the person who provided lodging for both Koutaro and the drifter to sell them out went down the drain as the pair had already left, leaving a thank you note. In an undisclosed hotspring, the drifter reveals his name for the first time; Akaomi Nanashi , which ironically literally translates as Nameless One. Other revelations include the fact Nanashi was once a samurai serving for a daimyo and one where he is not actually be Japanese to begin with, as he tries to cover it by dying his hair. After an encounter with two bumbling thieves, Nanashi and Koutaro head on full speed for Mangaku Temple.
After interrogating one of the captured Chinese envoy, the truth behind their presence in Japan is revealed. The Ming Emperor wishes to create a drug that would grant immortality and for that very purpose, they have traversed the seas in search of blood from a chosen child, who is none other than Koutaro himself. The tumorlous journey finally comes to an end, as Nanashi and Koutaro arrive at their destination, where they part ways. However in an unexpected turn of events, Koutaro is betrayed by the very monks he had came to seek help, as they turn him in to the Chinese envoy. It turned out to be a trap in more ways than one as the two members of the Chinese envoy find themselves surrounded by the daimyo's men who want Koutaro for himself. Realizing something amiss when he encountered a fleeing palace guard, Nanashi returns to the temple grounds only to find Koutaro has been captured. Though he tries giving chase, Nanashi is thrown off track as his trusty steed was injured in the pursuit. After forcing information out of the monks, Nanashi hastily undertakes a mission to rescue Koutaro with little time to spare. Meanwhile, Itadori, the commander of the daimyo's army, discovers that a bloodbath had took place, and he soon finds out that Koutaro had been taken to the Shishine Fortress, as well as the fact the palace has been massacred, with the daimyo kidnapped.
Amassing a huge army, Itadori arrives at the fortress, ready to tear it down. Attempts to slow them down proved futile, as Itadori simply kills off his lord, who was being used as a hostage, rallying the soldiers to lay siege. As the troops advance into the encampment, the Chinese easily fights them off, despite being much fewer in number. Despite all that, their numbers finally dwindle due to the constant onslaught, with Itadori confronting Rarou once again to settle things once and for all. Cue Nanashi, who finally arrives at Shishine, though he takes a moment to reflect on his past misgivings when he was still serving under a feudal lord. After coming to terms with himself, Nanashi makes a resolve to save Koutaro no matter what it takes. Possessed by the spirit of the wargod Bishamonten himself, Nanashi cuts down everything that stands before him until he had reached Koutaro.
After many deaths later, it was time for the final duel between Rarou and Nanashi, as they were the only ones left standing, with only one out of this two can emerge triumphant and claim the rights to being the strongest warrior.
Lawl, I'm not going to reveal how it all ends, but let's say an overused plot device is employed here. I put an entire week's worth of anime on the backburner for this and I'm glad to say it doesn't disappoint. While the plot is hardly the most original(LAWL SUPER MEGASTRUCTURE OF DOOM), the producers manage to pull off enough plot twists and surprises, to keep things fresh, making the journey from start to finish an exciting one, with no dull moments to speak of whatsoever. While they didn't develop the main characters that well, they however, did an excellent job playing on the cultural differences; a psychopathic foreigner with bloodlust against a guilt-ridden ronin with a bloodied past, possessing superhuman abilities. What else do you really need to know, when it's quite clear they were meant to fight one another taking into account their contrasting characteristics, with only the fact they're both GAIJINS that tie them together, which was the central theme to begin with. As expected from BONES, the animation was fluid, and special mention has to be made for the fight scenes, which although brief, were nicely fleshed out and concise, as each battle sequence feels fast and furious, and dissipates just as quickly leaving me breathless, with no sacrifice in detail. The final boss battle wasn't as awesome as I had hoped for, but it still provides a "clear cut" conclusion to the central characters' rivalries. Speaking of animation; gore fans, rejoice! There's lots of blood being spilled here especially during the final siege of Shishine, as the production team is unapologetic when it comes to violence. Decapitation, disembowelments, crimson fountains of blood, you name it, they have it here! I could go on ranting about how great the movie is, but I'll stop now since it's getting way past even the the tl; dr limits, so be sure to check this out!