Keychain | Jujutsu Kaisen | Inverted Spear of Heaven

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)