Tenko no Shinzui

Tenko no Shinzui (天瞽の心髄, Literally: "Quintessence of Heavenly Darkness") is an ethereal blade exclusively wielded by Nōsei. Brought into existence through extreme mastery of the Mikoto Clan's unique performance of the Nōsei claims that this sword is the representative of his very existence. Due to this Tenko no Shinzui exists as an extension of Nōsei himself, effectively blurring the line between technique and weapon. To this end it is thought to be distantly related to the items created through the Shadow Invocation, though this merely theorized and is likely impossible to verify. The blade itself appears pulsating strands of energy that weave together in what appears to be the shape of a curved blade.

While is a blade Nōsei he received from his mother, and serves as a powerful connection to his clan, Tenko no Shinzui is a blade that defines his own abilities and individuality.

Abilities
Being a blade completely composed of chakra Tenko no Shinzui possesses a cutting edge that challenges the highest levels of chakra flow. Additionally, Nōsei has determined it to be unnaturally durable, to the extent that Myaku-giri was unable damage it whatsoever. Regardless, it is likely its ethereal existence prevents the blade from sustaining permanent damage. Additionally, its existence is tied to Nōsei himself, prevent the sword from existing out of his direct possession. Despite this, Tenko no Shinzui can exists outside of the grasp of Nōsei, simply hovering around him in an incorporeal form. Nōsei can also dismiss the blade at any time; though re-invoking it requires more chakra.

While Tenko no Shinzui possesses extreme cutting potential its real usage stems from its ability to selectively cut targets based on the user's will. More specifically Nōsei can determine whether or not this sword interacts with the physical world or not. In this way he can allow the blade to pass through both objects without inhibition, as if the sword has no substance. Additionally, the entire blade doesn't have to embody the same quality. Thus, Nōsei could hypothetically "pierce" two targets simultaneously, but only harm one of them.

It should be noted that while Tenko no Shinzui takes a significant amount of chakra to invoke, it doesn't constantly expend chakra. This moderation of stamina wasn't inherently present, causing Nōsei to burn through extreme amounts of energy to utilize this blade. Particularly, it has taken several years for him to perfect its control. While this sword doesn't naturally expend energy the chakra it is composed of can be expended in order to perform chakra based kenjutsu and sword based ninjutsu. Energy expended in this manner weaken the blade's cutting potential depending upon the amount of chakra consumed, which cannot be resupplied without re-invoking the blade. Conversely, Nōsei can choose to not use the chakra in the blade and simply supply his own chakra to utilize this techniques through Tenko no Shinzui.

Finally, while Nōsei claims that his stamina permits the possibility of creating more than a single Tenko no Shinzui at once, such a feat is impossible. This, according to Nōsei, is due to the fact that the blade exists as a particular ethereal object, not merely the byproduct of the technique. This in turn supports why the Tenko no Shinzui only requires chakra to invoke, being a type of payment for its usage.