Nikkou

About
Nikkou is one of the only two swords on  The Continent  that can harm  Dark Lords  and the  Demon King  by shattering their  invincibility fields. She was originally a human samurai and one of The Legendary Five. She was born in the year GL0512 in JAPAN, over 1500 years ago. She met British and joined the group after her parents, siblings, village and everyone she held dear were slaughtered by a Dark Lord. She was described as a stunningly beautiful woman, with an incredible aptitude for swordplay and with an impeccable talent to remain calm at all times. Even Ho-Raga, who has no interest in women, admitted that he would have fallen for her if she had been born a man.

The group of the Legendary Five descended to the Ancient Ruins in order to find a method to break the invincibility field of the Dark Lords and challenge Demon King Gele. After they beat a prototype god, Supreme God Planner opened the God's Gate for them and took them to the land of the Gods. He met them there and decided that he would grand them one wish each as a reward for getting so far. Both Nikkou and Chaos wished to have the power to break the invincibility fields of dark lords and the demon king, but as a twist, both of them were transformed into Dark Lord killing swords. She was turned into a Katana (called the Holy Katana Nikkou) while Chaos was turned into a western style blade (called Demonic Sword Chaos).

In Kichikuou Rance, Nikkou could take human form, unlike Chaos who complained that the god is not fair because she can transform back to human form while he can't, even though they both wished the same wish to the god.

In the current canon, Nikkou doesn't have the ability to turn back into a human, but, like Chaos, retains the ability to speak.

She appeared for the first time in canon in Sengoku Rance, along with Kentarou and Miki Kurusu. Kentarou is Nikkou's wielder and is a very talented swordsman that can make the best of her. Chaos felt eager to kill Miki, since he claimed that he turned into a sword with the sole purpose of killing the Demon King and reproached Nikkou for helping them. Nikkou said that she felt pity for Miki because she didn't chose to become the Demon King, so she's willing to help them. She claimed that Chaos should be able to feel the same way.

List of wielders
Considering that Nikkou, like Chaos is now nothing more than a talking sword, in order to fight the dark lords and the demon king, she needs a wielder.

Several hundred years ago, Nikkou was wielded by a Hero of the world but during his combat with the recently freed dark lord Xavier, he turned twenty, lost his Hero powers and was killed by Xavier (though Xavier was sealed once again thanks to dark lord sealing techniques taught to members of the Tenshinism sect).

Later a hero used her in the "Operation: Bomb the Mazeel Line" to repel Dark Lord RedEye from the Mazeel Line and save Zeth from destruction.

Afterwards, it is unknown to whose hands she passed to, until eventually she was found by Kentarou in a bandit camp. After Kentarou somehow defeated the bandits, he took Nikkou as his own and has been Nikkou's wielder ever since.

Trivia

 * Since Chaos is listed as a Balance Breaker, it is entirely possible that she's also capable of holding the title, due to her ability to kill Dark Lords.
 * Her former Sword Combat skill is somewhat ironic, given her current condition.