Sun Blade

The Sun Blade (日輪, Nichirin, Viz: Nichirin) is the secret blade forged long ago on a continent that has sunk into the ocean.

The blade was said to have been passed down for generations within the council of swordsmen. Nichirin concealed the blade in the pocket dimension in his pearl necklace and gave it to Atomic Samurai before passing away in the battle against the Monster Association. It has a similar weapon known as the Moon Blade, as it's opposite.

The legend says that the warrior who is in the possession of the Sun Blade and the Moon Blade together will obtain unparalleled power. Bringing that legend to reality is the Council of Swordmasters's longstanding mission.

The Sun Blade retains a consciousness, telepathically linking itself with its wielder to determine their worth and whether or not they're worthy of the blade's power. If the Sun Blade deems the wielder worthy, it will grant them it's power. As seen with Atomic Samurai, the Sun Blade dramatically boosted his abilities, allowing him to slice one of Homeless Emperor's largest energy balls into several pieces and even cut off Golden Sperm's arm. When it grants the wielder its power, it also takes control over their consciousness, as Atomic Samurai noted. However, using too much of the blade's power can significantly weaken the user, as Atomic Samurai was significantly drained after clashing with Golden Sperm.

Trivia

 * The sword's literal name, "The Nichirin [Sword]" (spelled 日輪), is pronounced the same as the name of the swordmaster Nichirin (spelled ニチリン), with both meaning "The Sun." The swordmaster's name is spelled using hiragana while the blade is referred to by its kanji, differentiating the two in the manga's text. Because there is no official way to differentiate the two using the English alphabet, the fan translations as used by the wiki utilize the translated name for the sword but retain the Japanese name for the swordmaster, while the Viz translations use the Japanese for both.