Quick answer: To obtain Invertion in Jujutsu: Zero, you must reach Level 300 and speak to the Physical Heavenly Restrictor NPC to accept and complete the Invertion I quest.
In Jujutsu: Zero, character progression relies heavily on completing specific milestones to unlock advanced abilities and items. Players pursuing the Heavenly Restriction path—often associated with the Toji clan and high physical stats—eventually encounter the need for Invertion. This resource is locked behind a mid-to-high-level questline that requires significant time investment to access.

Prerequisites for Invertion
Before attempting to acquire Invertion, you must meet a strict level requirement. The quest provider will not interact with you meaningfully until you have reached Level 300. If you are below this threshold, focus on completing story quests, daily missions, or farming curses to gain the necessary experience.
Locating the Physical Heavenly Restrictor
The key to obtaining this item lies with an NPC named the Physical Heavenly Restrictor. This character manages the progression for players who have opted out of Cursed Energy in favor of raw physical prowess. Once you meet the level criteria, locate this NPC to initiate the dialogue for the next stage of your development.

Completing the Invertion I Quest
Upon speaking to the Physical Heavenly Restrictor at Level 300 or higher, you will be offered the Invertion I quest. Accepting and completing the objectives of this specific mission rewards you with 1 Invertion.
This resource is typically a critical component for players building towards the Inverted Spear of Heaven, a weapon ranked highly in the current meta (often placed in A-Tier or higher alongside the Dragon Bone). This weapon is favored for its multi-hit attacks and ability to stun bosses, making the acquisition of Invertion a priority for offensive physical builds.