Kurobikari

The Kurobikari (黒光り, Black Lustre), is a sword initially created to destroy the Shinju. After unsuccessful attempts, this sword was thought to be lost under the depths of the earth. It is noted to have hundreds of souls within it, and anyone who wields it gains the power of these combined souls. Kurobikari is the polar opposite of the Shōten, which was created for a similar objective.

History
During the time period when the Shinju rampaged around earth, an unknown prideful clan that lived through the carnage of the Shinju became fed up with the destruction it caused. The death of numerous clan members and annihilation of other clans created a sort of competition for the clan. At this time period this clan was the most notorious and strongest clan of their region if not the entire continent. This clan thrived off of battle, going to war with other clans to display their dominance. The clan was prosperous, having thousands of members and ginormous amounts of lands. However, after the Shinju's rampage, this clan's prosperous life was decimated. Their lands reduced to nothing but ashes and their numbers dramatically reduced to mere hundreds compared to the thousands once had. A hatred grew in them, each member wanted to rid of the Shinju and to do so they came up with the plan to create a sword of pure evil that could face off against the Shinju and destroy it. To help them with this plan was none other than an evil shaman who created a blade of magical material. Each clan member would sacrifice themselves in order for the Shaman to place their souls into the blade. After the blade was crafted, the Shaman attempted to wield it only to be nearly killed by the sheer power of the blade. Deeming it too powerful, he attempted to destroy it only to come to the realization that this sword could not be destroyed. Alternatively, he placed the blade in a case, placing it into a relic where it wouldn't be found.

After centuries upon centuries of natural and supernatural occurrences, the relic was covered deep into the earth. That was until a massive earthquake unearthed the relic but, the sword would lye there for several more centuries until it was found by Iori Hyūga.

Abilities
Sealed with the souls of hundreds of people, the Kurobikari has an incredible power that can be harnessed by anyone who wields the blade. The Kurobikari can only be used by one person and that person is to give their blood to the blade and commit their soul to it in case their are to die. If another person were to attempt to wield the blade, their soul will be absorbed into the sword, adding to its power. Not only that, they will be influenced by the evil souls already inside of the blade.

Initially, the blade was intended to be able to cut the Shinju in half with pure force.