Keychain | Jujutsu Kaisen (See Variants)

The Inverted Spear of Heaven is a spearhead with a shortened handle (thus resembling a large dagger) and a two-pronged, jitte-like blade. It has a q-shaped, rounded hand guard that points out on the side of the longer blade. Additionally, the weapon has a black handle with a circular link at the end that allows it to be connected to metal chains. It appears a third blade may have been located on the front of the weapon, but it has evidently been broken off.

The weapon has been imbued with a cursed technique powered by a special, foreign type of cursed energy, which grants it the following effect: the "forced cancellation" of active cursed techniques. If a wielder's target or their jujutsu is directly hit by the Inverted Spear of Heaven, their technique will be immediately nullified. Even powerful cursed techniques like the Limitless can be completely invalidated by this weapon.

Toji Fushiguro possessed the Inverted Spear of Heaven and kept it within his inventory curse with the rest of his cursed tools. This allowed him to take out the Inverted Spear of Heaven at any time. 

(from Fandom Jujutsu Kaisen Wiki)

Jujutsu Kaisen (from Jujutsu Kaisen Wiki)
The story of Jujutsu Kaisen is set in a world where Cursed Spirits feed on unsuspecting humans and fragments of the legendary and feared demon Ryomen Sukuna have been lost and scattered about. Should any curse consume Sukuna's body parts, the power they gain could destroy the world as we know it. Fortunately, there exists a mysterious school of Jujutsu Sorcerers who exist to protect the precarious existence of the living from the supernatural!

Ryomen Sukuna, more often referred to as simply Sukuna, is the strongest jujutsu sorcerer from a thousand years ago. Regarded as the undisputed King of Curses, Sukuna is one of the primary antagonists of the Jujutsu Kaisen series. According to legend, Sukuna was an Imaginary Demon during the Heian Era but in truth he was a sorcerer also known as the Disgraced One. Jujutsu sorcerers of the Golden Age of Jujutsu gave their all against him but ultimately fell one after another. Sukuna existed throughout the ages by transforming into a cursed object after death, a state where he split his power into twenty indestructible fingers. Sukuna was incarnated in June 2018 when Yuji Itadori consumed one of his fingers. Sukuna was trapped inside Yuji's body and was rarely in control until he managed to transfer his soul into the body of Megumi Fushiguro. 

(from Fandom Jujutsu Kaisen Wiki)