Jack's Sword
| “ | "This blade was forged from the righteous energy within thee. It possesses the power to destroy this evil force. But be warned, this evil is not of the human world. It has magic beyond your understanding. Trust not what you see, but what you feel." | ” |
—Odin, Ra and Vishu, Episode XXXVIII: The Birth of Evil, Part 2 | ||
Samurai Jack's katana, originally the Emperor's katana, is a magic katana forged by the three gods Odin, Ra and Rama for the sole purpose of destroying Aku, and the only weapon capable of doing so.
Background
Origin
The katana being forged
When Aku invaded Earth, the gods Odin, Ra, and Rama forged the katana from the power of righteousness within the Emperor's heart. Its divine nature is capable of inflicting burning wounds to Aku, which are very difficult for him to regenerate from. Enough hits with the katana essentially negates Aku's ability to regenerate from his wounds, at which point further damage could presumably either kill him or seal him away again. The katana can only be used for good; in the hands of evil, it cannot harm an innocent. This was first demonstrated on one occasion where Aku stole the katana and attempted to kill Jack with it. Instead of stabbing Jack, the katana simply struck Jack's chest without causing any harm at all.
However, this property appeared to apply only to biological lifeforms and not to robots, as Jack, when infected by Aku's essence to become Jack-Aku, either killed or grievously harmed an innocent robot with the katana, but appeared not to be able to kill the Lizard Monks whom he struck with it, only rendering them unconscious like a club would.
Very few characters other than Jack use the katana in the series, most notably the King of the Spartans in Episode XXV: Jack and the Spartans, after his own sword was broken and Jack threw him the katana to protect himself. It was also revealed in Episode XCIV that the Emperor had used the katana to kill bandits that threatened him and his family after they refused to leave them in peace.
Season 5
At some point over the next 50 years, Aku began actively destroying all of the world's time portals. After he foiled Jack's attempt to use the last of them and destroyed it, the dark sorcerer mutated three innocent goats into monsters for Jack to fight. Overcome with rage and despair, Jack killed the mutated goats, only to stare in horror when he saw what he had done. The sword fell from his hand, and fell into the pit where the time portal had been, out of Jack's reach.
In Episode XCVIII, Jack, who had regained his will thanks to his new friend and ally Ashi, descended the pit with the help of a large bird. The katana was nowhere to be found, and Jack understood that he hadn't lost the sword; rather, the sword had left him. After leaving the pit, he went to the cliff's edge and entered an astral plane by meditation. After a journey, he realized that his anger had consumed him, and vanquished the personification. Having regained balance, the three gods restored Jack to his former self, full of confidence and hope, and returned the sword to him after infusing it with his own righteous spirit, making the blade even more powerful.
In Episode C, Aku confronted Jack, having learned from Scaramouche that he had lost the sword, the assassin unaware that he had reclaimed it in the meantime. Aku killed Scaramouche and made to leave upon realizing his mistake, but deduced Ashi's heritage, and turned her against Jack. The samurai used the sword to defend himself, and after a slight cut to her corrupted form, she begged Jack to destroy him. He was unable to, and dropped the sword as he fell to his knees in defeat. Aku seized the blade in triumph.
In the finale, Jack and his sword were held up in different parts of Aku's lair. When Jack's friends broke him free, he attempted to reclaim the sword, only for Ashi to stand in his way. Once Ashi succeeded in breaking free, while keeping Aku's powers, she stretched her arm out and grabbed the sword (oddly, though she grabbed it by the blade, she was not hurt despite using Aku's powers), handing it to Jack before opening a portal back to the past.
Upon returning to Aku's lair in the past, Jack struck ruthlessly at Aku, vanquishing his essence bit by bit, despite his attempt to flee. As the last remnant of Aku attempted to run away, Jack stabbed him from above, imprisoning his essence in the blade. With a final strike to the ground, the darkness of Aku spread throughout his lair before exploding, leaving only a crater and destroying the threat of Aku forever.
After Aku's demise, Jack still keeps the sword for future use.
Powers
The katana has the power to cut through any mundane substance, given that there is enough force behind it (Jack was, for instance, unable to cut through the adamantium armor of the Ultra-Bots in episode XVIII without artificial strength enhancement). The katana is able to vanquish mystical beings that cannot be slain by conventional means such as the Minions of Aku, The Sirens and the evil spirit of the Well of King Ozric. Those beings were vaporized after being slain with the katana.
Likewise, similar magically enhanced objects can also prove immune to being cut by the katana (for instance, the Scotsman's blade was imbued with magic runes and proved to be too resilient for Jack to destroy). The katana is incapable of harming and destroying beings of divine origin such as the Minions of Set. The katana is also incapable of destroying the magical orb that imprisons the Fairy.
The katana itself, possibly due to its divine origin, seems to be essentially impervious to harm; it will simply rebound off of substances that it cannot harm instead of shattering upon impact, and can be used to block or deflect virtually anything without suffering damage. Unlike more mundane katana, which require extensive maintenance, Jack's katana appears not to require any sort of upkeep, though Jack was shown sharpening it on one occasion.
The katana's main purpose is to destroy Aku and defend the innocent; however, one very important aspect that Jack had failed to consider in his first battle with Aku, was that the sword is still just a tool, whose true power depends on its wielder. Likewise, its wielder must be pure in heart, or else they will be unable to use it, as shown when it abandoned Jack when he gave in to his anger.