Kento Nanami's Powers From Jujutsu Kaisen Explained
The pilot episode of standout 2020 anime "Jujutsu Kaisen" introduces viewers to Yuji Itadori, an athletically-gifted but otherwise relatively normal high schooler. Then, over the course of the series' first episode, Yuji learns of the existence of supernatural Cursed Spirits, or Curses, which are malicious manifestations of negative human emotions.
Yuji ends up enrolling in Tokyo Prefectural Jujutsu High School, an academy that teaches its students how to utilize Cursed Energy, a supernatural human resource, to become Jujutsu Sorcerers and battle Cursed Spirits. Early on, Yuji learns that the world of Jujutsu Sorcerers and Curses is organized into a sort of hierarchy, through which Jujutsu Sorcerers are assigned grades correlating to their strength. Those are then used to ensure appropriately powerful Sorcerers are assigned to battle Curses of corresponding power.
As part of Yuji's education, his mentor Gojo entrusts him to investigate a supernatural murder of three high school students in a movie theater. Since he expects the responsible Curse to be beyond Yuji's power level, Gojo assigns fellow school staff member Kento Nanami to accompany Yuji on the mission. Over the course of their time battling alongside one another, Yuji comes to learn the full extent of Nanami's considerable power, which is largely oriented around a single, powerful ability.
Nanami's signature ability is the Ratio Technique
Nanami first reveals his combat prowess in a battle that follows his and Yuji's initial visit to the movie theater at which the murder they're tasked with investigating took place. There, Nanami notices visible remnant evidence of the presumed assailant's Cursed Energy. They follow its trail onto the roof of the movie theater building, where they run into two Curses. Nanami decides that he and Yuji will take on one Curse each.
Naturally, given that he's the more seasoned fighter, Nanami dispatches his Curse first. To do so, he makes use of an ability he calls the Ratio Technique. In short, Nanami is capable of visualizing parts of his opponent's body divided into ten equal parts. By activating this technique, he creates a weak spots on the seven-to-three points of each of those body parts — meaning either 3/10 or 7/10 on his visualized graph, depending on which end is considered zero. Hitting that weak point, then, causes massive damage.
The only weapon Nanami wields in combat is a dull knife
When Nanami activates his Ratio Technique for the first time in battle alongside Yuji, he strikes his Cursed Spirit opponent with a knife bearing a short, fat blade, more closely resembling a butcher knife than a traditional combat weapon. Furthermore, his blade is wrapped up completely in white bandages patterned with nonuniform black spots.
While explaining the Ratio Technique to Yuji, Nanami mentions that the power added to his attack by merit of finding his enemy's weak point makes it such that even a blunt weapon can cut like a sharpened sword. His knife, then, may indeed be a kitchen implement with its cutting edge dulled further by the bandages wrapped around it, but with the Ratio Technique it becomes capable of slicing powerfully and precisely. Furthermore, since the knife is otherwise useless in battle, his choice of weapon reinforces the fact that he can use the Ratio Technique adeptly enough that a better weapon is unnecessary.
Explaining the Ratio Technique makes it stronger
While the Ratio Technique may essentially be Nanami's means through which to damage his opponents, the ability can become stronger if used in tandem with one or multiple Binding Vows. The idea of a Binding Vow — essentially a magical agreement — is introduced in "Jujutsu Kaisen" Episode 6, in which a dead-at-the-time Yuji makes an agreement with Sukuna, the King of Curses that he will come back to life in exchange for Sukuna's ability to take over Yuji's body at will for short intervals.
Nanami's Binding Vows aren't made with another party, but rather conditions he sets for himself that affect his combat capabilities when fulfilled. In his fight alongside Yuji against the Cursed Spirits duo, Nanami fulfils a Binding Vow called Showing One's Cards, which stipulates that explaining how a technique works makes it stronger. Nanami, then, both reveals the details of the Ratio Technique to Yuji in their first fight alongside one another while simultaneously increasing his power level.
Working Overtime unleashes Nanami's true potential
Following their bout with the pair of Cursed Spirits, Yuji investigates a boy named Junpei who seems to be tied to the murder while Nanami tracks down an extremely powerful cursed spirit named Mahito, who is directly responsible for the killings. When Nanami first enters into his fight against Mahito in "Jujutsu Kaisen" Episode 10, he expresses wanting the battle to end quickly so that he doesn't have to work overtime.
At first this seems to be in reference to his past as an office worker. Early on, Nanami is described as an "ex-salaryman," who left behind his office job to fight Cursed Spirits. However, his mention of Overtime turns out to be a reference to another Binding Vow with which Nanami powers up considerably during his fight against Mahito. In short, should Nanami actively battle an opponent outside the confines of his scheduled shift working for Jujutsu High, which ends at 6:00 PM, he benefits from a massive increase in the amount of Cursed Energy he can wield in combat.
Nanami's Ratio Technique becomes far more formidable during Overtime
When Nanami activates Overtime in battle against Mahito, he removes his tie — which bears a similar pattern to the bandages wrapped around his knife, suggesting that it serves a similar function in combat — and wraps it around his right hand. Nanami then becomes capable of using a souped-up version of his Ratio Technique called Collapse.
Whereas the vanilla Ratio Technique relies on Nanami visualizing a sort of graph and striking a particular point on that graph with a fine edge, Collapse throws those rules out the window and simply allows Nanami to inflict large-scale, massive damage. Rather than requiring an auxiliary weapon, Nanami can simply activate Collapse with his necktie-bound fist. And instead of localizing its impact to a single weak point, Collapse affects a large area, shattering an entire wall when deployed against Mahito.
This remains the peak of Nanami's range of abilities as depicted in "Jujutsu Kaisen" thus far. Those curious how much damage Nanami's Collapse could inflict on a Cursed Spirit rather than a brick wall will have to hope he returns to battle in "Jujutsu Kaisen" Season 2.