Ultra Instinct is the ultimate martial arts technique within Dragon Ball franchise. Widely known as the inherent state of being for the angels of the multiverse, this fabled technique is notoriously difficult to learn for anyone outside of this powerful race, even if they are as powerful as the Gods of Destruction.
The main reason it is such a difficult concept to grasp is that the user must be in a perfectly calm and stable state of mind, whereby their body reacts to danger on its own. Although Goku is the only person in the Dragon Ball aside from the angels who have been able to fully utilize it, certain characters would be the perfect candidates to eventually unlock it for themselves.

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5
Gohan could potentially have unlocked this technique
A separate path to power
After the Tournament of Power and Granolah arcs, fans were convinced that it was only a matter of time before Gohan would go on to unlock Ultra Instinct. Although his incredible Beast form was what fans got instead, a large number of fans believe that it could still be possible in the future.
Although unlikely, one wouldn't be wrong to assume the connection between Gohan and Ultra Instinct from a basic perspective. Since Ultra Instinct requires calmness and control above all else, Gohan lends himself well to the technique due to the restraint he has shown against powerful villains, as well as his cerebral nature.
4
Master Roshi already seems to have a handle on the technique
Goku's legendary teacher
It is safe to say that Goku would not have even come close to where he is without the direct influence of Master Roshi, who is known as one of the greatest martial artists in the universe. Although his power was already formidable, the real reason why he is a prime candidate to learn Ultra Instinct is that he already had something quite similar.
We noted that the most important thing one needs to use this technique is a calm heart and mind, so that the user can fully immerse themselves in battle. Although he is well beyond his age, Roshi's calm nature allowed him to instinctively dodge a barrage of attacks from Jiren, making him the closest mortal to achieving Ultra Instinct after Goku himself.
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3
Uub is a good candidate for achieving ultra instinct
A latent powerhouse
As the human and pure reincarnation of Kid Buu, Uub was born due to Goku's wish at the end of the Buu Saga. As such, he is also the recipient of an immense amount of divine energy, which he received from the time when the Great Supreme Kai was absorbed by Majin Buu. Because of this, many believe him to be the perfect candidate to achieve Ultra Instinct.
IN Dragon Ballthe human characters haven't really been significant for quite a while now, aside from maybe Krillin. Considering how Ultra Instinct is a technique rather than a species-specific transformation, it would make Uub the perfect person to use it alongside Goku, especially given his immense latent strength as Kid Buu's reincarnation and the well of Divine Ki he already possesses.
2
Jiren would make a great ultra instinct user
Universe 11's greatest warrior
Out of everyone on this list, it's very likely that Jiren will have already unlocked Ultra Instinct by the next time we meet him. The main reason for this is that his composure in battle and unmatched Ki control make him an obvious choice for someone to unlock the technique in the first place.
Furthermore, his fight against Goku at the end of the Tournament of Power Arc has shown him the power of this technique, as well as the fact that it is possible for a mortal to learn it, so it is very likely that he has been training relentlessly since the tournament to achieve even greater strength through Ultra Instinct. Through this, it would be the best way to reintroduce Jiren to the story.

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1
Beerus can already use a Basic Ultra Instinct version
The strongest destroyer
It likely comes as no surprise, Beerus is the closest character to getting this technique, and in fact he's already shown the ability to use it. During the Destroyer exhibition match, all the Gods of Destruction simultaneously jumped on Beerus, but he managed to take them all on thanks to his strength, tactical brilliance, and use of Ultra Instinct.
But admittedly, his use of the technique is very basic, as he uses it in its Ultra Instinct Omen state, which was even surpassed by Goku. Still, his use of it shows that he already has a talent, so it's only a matter of time before he can master it and utilize it fully to become the strongest being in the multiverse.
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