Jujutsu Kaisen's Domain Expansion stands as the pinnacle of Jujutsu due to the immense benefits it offers. Unique to each sorcerer, it appears as a physical manifestation of the user's mental landscape and Innate Technique within a barrier. What makes it so deadly is the sure-hit effect that one receives upon successful activation of the technique.
For the same, hand signs are necessary. As seen in many cases, sorcerers like Yuta Okkotsu and Megumi Fushiguro used various hand signs to activate their Domain. Even Ryomen Sukuna needed a pair of hands to use Domain Expansion. Meanwhile, only Gojo Satoru stood as the exception - his Infinite Void could be activated with a single hand, a detail that set him apart from others.
However, throughout the 271-chapter story, it was never touched upon as to why or how he could do that.
Disclaimer: This article is speculative in nature and reflects the author's opinion.
Jujutsu Kaisen: The major detail that distinguishes Gojo from other Jujutsu sorcerers, explored
As mentioned, in order to use Domain Expansion in Jujutsu Kaisen, hand signs are necessary. They are unique to each user of the technique and are believed to be based on Hindu and/or Buddhist symbolism. Activating the technique expands the user's Innate Domain, materializing it and deploying their Cursed Technique within an enclosed space, usually a barrier.
Apart from Sukuna, whose Domain possessed no barrier, each sorcerer's Domain had a barrier that was effective. But again, a major detail made Gojo an exception to the technique. He was the only known sorcerer to be able to deploy Domain Expansion through a sign using a single hand, while even the Demon King used a pair of hands.
In fact, Sukuna had two extra arms to be able to weave hand signs during fights to make him a more formidable force. However, Gege Akutami never touched upon how Gojo was capable of such a feat. As seen for the first time when Gojo fought Jogo, he didn't require his other hand at all, which was either holding Yuji Itadori or simply reaching to pull down his blindfold.

There could be a single, multiple, or no reason at all behind this. Assuming there is some lore behind it, it could be that this is a feature of the Gojo Clan. Coming from a powerful clan like his, Gojo must have learned some secret technique that allows him to pull this off.
On the other hand, there is a possibility that he himself figured out how to simplify this technique, which was something he spoke of wanting to decipher during the Hidden Inventory arc.
Another reason could be that he was simply a genius. Being the only one in 400 years to inherit both the Six Eyes and Limitless likely came with perks, and this could be one of them. Whatever the reason may be, a major detail like this is another point as to why Gojo was the strongest.
Furthermore, likely to show his acknowledgment of Gojo, Sukuna used the same hand sign towards the end of the Shinjuku arc. It can be seen as an "Imitation is the greatest form of flattery" sort of situation. While Sukuna didn't really admire him, it is undoubted that he had acknowledged Gojo for pushing him to the limit.
Another point is that this could tie into Hindu Mythology - Gojo was often likened to Indra, a powerful deity, and thus, to parallel it, he required a single-hand sign, signifying his status and genius in Jujutsu.
Final thoughts

Gojo Satoru’s ability to activate Domain Expansion with a single hand remains an unexplained yet significant distinction in Jujutsu Kaisen. While most sorcerers, including Sukuna himself, needed both hands to form the necessary signs, Gojo’s mastery set him apart. This could be attributed to his exceptional genius, his lineage in the Gojo Clan, or possibly a hidden technique he deciphered.
Furthermore, links to Hindu mythology and his parallel to Indra simply reiterate his unmatched status. Despite the story’s 271 chapters, Gege Akutami never furnished a proper explanation for the same, opening doors to speculation. Sukuna’s decision to mimic Gojo’s hand sign during the Shinjuku Showdown arc likely testifies to his strength, reinforcing Gojo’s legacy as the strongest sorcerer.
Be it natural prowess or secret knowledge, this small yet impactful detail will remain a source of intrigue, solidifying Gojo’s legendary status in Jujutsu Kaisen.
Related links:
- Gojo might be the most misunderstood Jujutsu Kaisen character
- Jujutsu Kaisen epilogue proved Gojo's students truly cared for him
- 25 most memorable Gojo quotes from Jujutsu Kaisen, ranked