Sukuna's Powers From Jujutsu Kaisen Explained
The first episode of the supernatural action anime series "Jujutsu Kaisen" revolves around a Cursed Object that turns out to be one of the fingers of the legendary Cursed Spirit Ryomen Sukuna. In the parlance of "Jujutsu Kaisen," a Cursed Spirit is a monstrous — sometimes humanoid, sometimes creature-like — entity manifested from one of the many ills of the human world. Sukuna was technically defeated prior to the start of the series, but given his considerable power, defeat meant not total eradication but simply that his presence would remain in the 20 fingers of his four arms, which are essentially impossible to destroy and remain in the world at large.
In order to protect his school from destruction and save the life of Jujutsu Sorcerer Megumi Fushiguro, high-schooler Yuji Itadori swallows one of Sukuna's fingers in Episode One. This serves as the series' inciting incident, introducing Yuji to the world of Jujutsu Sorcery — the use of magical superpowers to fight Curses. Likewise, this act revives Sukuna in a sense, providing his spirit residence in Yuji's body. While the Sukuna of the past is described as a generationally powerful force, however, the version of him manifested through one (eventually a few) of his fingers in Yuji's possesses a shadow of his full capabilities. Nevertheless, the present-day Sukuna of "Jujutsu Kaisen" is extremely formidable, and capable of a wide range of powers.
Sukuna can possess Yuji's body
The primary means through which Sukuna can affect the world in "Jujutsu Kaisen" is through possessing Yuji's body. The first time he does so is immediately after Yuji swallows his finger. At that moment, Yuji is about to be consumed by a Cursed Spirit attempting to secure the power of the finger for itself. Yuji swallows the finger instead in order to absorb its powers and give himself a fighting chance. Sukuna, in Yuji's body, then promptly dispatches the Cursed Spirit. Satoru Gojo, a supremely powerful Jujutsu Sorcerer, shows up to the scene shortly after, ready to kill Yuji and exorcise Sukuna. However, he determines that among Yuji's abilities is the power to suppress Sukuna at will, and allows him to live.
In Episode 4, Yuji wilfully allows Sukuna to possess his body again to survive an encounter with another formidable Curse. Sukuna's powers are such that, when he has control of Yuji's body, he retains some of his abilities from when he was a discrete entity, meaning that in this situation too, Sukuna makes quick work of the foe. This time, though, Yuji must pay a price — Sukuna kills Yuji, and only revives him once Yuji agrees to a pact through which Sukuna is allowed to possess him for minute-long intervals, leaving Yuji with no memory of his possession. While this hasn't yet happened in the "Jujutsu Kaisen" anime, it remains a threat moving into Season 2.
Sukuna can incarnate on Yuji's body
Short of possessing Yuji fully, Sukuna can still manifest himself in the real world through eyes and mouths on Yuji's body. After consuming Sukuna's finger, Yuji gains a couple of slits below each of his eyes. While they remain closed for the most part, they open when Sukuna possesses Yuji's body, and generally provide Sukuna something of a permanent presence on Yuji's person.
Meanwhile, Sukuna can virtually speak whenever he so desires by manifesting a mouth on Yuji's body, typically either below one of the eye slits or on one of Yuji's palms. The former he does, for example, in Episode 2, when Yuji enrolls in Tokyo Prefectural Jujutsu High School, prompting Sukuna to threaten its staff. Later on, in battle with Mahito — a powerful Cursed Spirit attempting to ally himself with Sukuna — he speaks to both Yuji and Mahito through a mouth on Yuji's face as well. Near the end of the "Jujutsu Kaisen" Season 1 finale, meanwhile, Fushiguro hands Yuji one of Sukuna's fingers for safekeeping. While the plan is to return it to Jujutsu High, Sukuna manifests a mouth on Yuji's palm and eats it himself, amplifying his powers as he lays somewhat dormant in Yuji.
Sukuna can instantaneously heal the human body
At the start of "Jujutsu Kaisen" Episode 4, Yuji and his classmates Fushiguro and Nobara Kugisaki are sent to a juvenile detention center to rescue any survivors following the appearance of a Cursed Womb, which is a sort of incubator for a Cursed Spirit. As they find out upon their arrival, an extremely powerful Curse has already emerged from that Womb and killed virtually everyone at the facility. Furthermore, Yuji, Fushiguro, and Nobara are ill-equipped to deal with a Curse of such power. Nevertheless, Yuji pushes himself to attack and promptly loses his hand in the process.
Yuji allows Sukuna control of his body in order to attempt to survive this encounter. Initially, Sukuna implores the Curse to work under him, but the Curse isn't having it and lashes out at Sukuna. To deflect the Curse's blast, Sukuna regenerates Yuji's hand and uses it to create a protective barrier. His regenerative skills are so habitual that he chalks healing Yuji's hand up to an accident.
Then, in the wake of that fight, Sukuna kills Yuji by removing his heart, which Sukuna doesn't require to live given his supernatural nature. This is something of a bargaining chip Sukuna then uses to form a pact with Yuji, allowing him free reign to take control of Yuji's body at will. After forming their pact, Sukuna demonstrates the full extent of his considerable healing powers, bringing Yuji back from the dead.
Sukuna possesses immense physical strength
The first time viewers witness Sukuna in battle is in Episode 2, when Gojo tests the revived Sukuna's capabilities through a quick fight between the two of them, with the latter in Yuji's body. While he is able to dodge Sukuna's subsequent series of physical attacks with ease, Gojo is the most powerful Jujutsu Sorcerer in "Jujutsu Kaisen," so the fact that Sukuna can even begin to challenge Gojo is evidence enough of his considerable strength.
Then, versus the powerful Curse in Episode 4, Sukuna begins his offensive with a series of physical blows. These attacks culminate in Sukuna ripping the Curse apart and embedding his severed limbs in an adjacent stone wall. Given that this Curse was just previously shown to be too powerful of an opponent for Yuji to even begin to attack, Sukuna is demonstrably stronger than Yuji many times over, despite relying on his body to survive.
Finally, in that fight's wake, Sukuna battles Fushiguro, who hopes to defeat him so that Yuji can regain control of his body. Sukuna remains dominant throughout this battle while only using physical attacks, seeming to hold back his presumably more powerful Jujutsu abilities after deciding that he finds Fushiguro personally fascinating, which he expresses midway into their fight. Nevertheless, it takes no more than his physical attacks to handily defeat Fushiguro before Yuji ends the fight by wresting back control.
Sukuna is unstoppable in his Innate Domain
Whenever Yuji communicates with Sukuna's spectral form, the latter appears on a throne of skulls in a dark, bloodlike lake. It's here, in his Innate Domain — a constructed environment that amplifies its creator's powers — that Sukuna is strongest.
The first time Sukuna demonstrates his power in his Innate Domain is in combat against the Cursed Spirit at the juvenile detention center. As his coup de grace, Sukuna activates his Domain Expansion Technique, which is essentially a means through which Jujutsu Sorcery users manifest their Innate Domain in the real world. He inhabits the Malevolent Shrine after which his Domain Expansion is titled for but a moment, after which the Curse is bisected into five slices that then burst into flame.
Later, in Episode 6, Sukuna wagers the pact he intends to make with Yuji on a fight between the two of them, which takes place again within his Innate Domain. Sukuna ends their battle in seconds, beheading Yuji's spectral form, before reviving Yuji's physical form upon their pact's completion.
Finally, Sukuna attacks the powerful Cursed Spirit Mahito in his Innate Domain in response to Mahito utilizing his unique relationship to the Soul to connect with Sukuna's spirit form directly. Sukuna retaliates by drastically injuring Mahito with a flick of his wrist, necessitating his retreat. This serves as yet another instance of Sukuna exhibiting his massive power, even as a mere spirit inside of a human vessel.