Over the years, fans have seen many strong characters in him Jujutsu Kaisen. In fact, when it comes to fight scenes, hardly any modern shonen does it better than Jujutsu Kaisenwith Gege Akutami gives us a battle to look forward to almost every chapter. These incredible characters are heavily featured in these amazing battles, but sometimes, sometimes, the plot requires them to be nerfed for one reason or another.
This is not an uncommon practice in the stories, and many times it serves the narrative very well, even if fans of those particular characters aren't too thrilled about it. Jujutsu Kaisen has unnerved many characters in various ways over the years.
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Mai Zenin
Mai Zenin is Maki's sister, and at first fans felt she didn't have much potential. However, when we saw Yorozu use a similar technique to her, the Construct, we knew that Mai actually had an incredible ability up her sleeve that she hadn't been able to fully utilize.
Of course, Mai wasn't nervous in the normal sense. She was never able to fully utilize her ability because she was born as a twin, which is considered a curse. In this sense, Mai was not technically unnerved by the author, but by fate itself. However, she still had the strength to learn. If the author allowed her to hit her true levels, then she would surely be among the most powerful wizards of the current era, and that goes without saying.
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Yuta Okkotsu
Yuta Okkotsu is an incredibly powerful wizard. He's actually a special class wizard, one of only four, and certainly up there with the best. Despite everything, Yuta was nervous on many occasions Jujutsu Kaisen. He has one of the most incredibly overpowered abilities fans have seen in the series, Copy. Unfortunately, he can only use copy for 5 minutes, which is a huge nerf.
Additionally, when Yuta expands his domain, called Authentic Mutual Love, he cannot choose which abilities to use, despite being able to deal lethal damage to his enemies. On the plus side, he can use whatever ability he ends up choosing over and over again if he chooses them. Still, Yuta, a mage said to have the potential to one day reach Gojo's level, was clearly nervous to prevent him from being too overwhelmed.

Jujutsu Kaisen finally reveals the official ending for its main trio
Gege Akutami's original trio of Jujutsu Kaisena has officially met its true end in the latest edition of Modulo Volume 3.
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Yuji Itadori
Yuji Itadori is the protagonist of the series, and even though he didn't have an obvious talent until much later in the story, we now know that he is actually an individual with the potential to reach Sukun's level. Yuji is actually very strong, wielding soul damaging punches and those alone should be strong enough to defeat the vast majority of wizards. In fact, even in his battle against Sukuna, this ability of his was greatly impaired.
Despite Yuji landing several black bolts on Sukuna, Sukuna's cursed energy levels, which were obviously supposed to drop, were preserved. This means that Yuji's ability to damage souls has been greatly impaired. If that wasn't enough, then it turns out that Yuji, who is also a Blood Manipulation user, does not yet have a perfect command of this ability. If he was allowed to use Blood Manipulation to the best of his ability, then the battle against Sukuna would be even easier for him. In addition, Yuji, who also has access to the Shrine, was given a different version of this technique by the author. His ability wasn't as dangerous as Suku's in Shinjuku, which again felt like another nerf from the author.
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Ryomen Sukuna
The Curse King, Sukuna himself has been nerfed on numerous occasions. After the battle against Gojo, Sukuna was nervous in many ways. For one thing, he was unable to properly utilize the reverse curse technique. At the same time, he couldn't even expand his domain for a long time when other wizards raided him. If Sukuna could go all out, the battle would be over in minutes.
Fortunately, much later, Sukun's domain returned to him and this allowed him to deal deadly damage to his enemies. Still, until the very end, Sukuna was far from the best and remained nervous until he died. If Gojo hadn't weakened him for Yuji, Sukuna would have wiped him out in minutes.
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Gojo Satoru
Gojo Satoru, the strongest modern wizard, has also been nerfed on numerous occasions in the story. The last time Gojo was nervous was in his fight against Sukuna, where despite being able to recharge his burnout curse technique over and over again, Gojo was shown to have hit his limit for plot purposes. If that wasn't enough, Gojo was also unable to make the most of Six Eyes, which should give him the ability to look at cursed energy at its innermost level. He was unable to dodge Sukun's World Splitting Dismantle, which characters like Kashimo and even Maki were able to dodge.
He was also unable to use the Reverse Cursed Technique after being hit by World Splitting Dismantle, despite regaining access to it. Gojo was undoubtedly very nervous in this battle to allow the plot to progress.
All chapters of Gege Akutami's Jujutsu Kaisen are available to read through Manga Plus.