Yuki can NOT affect souls let this be the standard
Okay so I've seen many people say this and I'm tired of it
The common argument is that she has soul perception The argument is she was able to hear the souls of past star plasma vessels The fact that she's a star plasma vessel herself And the fact that she wrote a book on souls
At most this would give her basic soul perception and she'd be able to fight with SSK but I'm far fetched on even this and I'll explain why But that's the most she'd be able to do
She can't injure mahito by attacking his soul like Yuji
She can't affect incarnated sorcerers She can't heal soul damage to herself
Okay so let's start
The first picture shows that Gojo is able to see the soul in the exact same way mahito does
Yet he cannot affect the soul in the same way Yuji does in his fight against Sukuna
Nor do they give him SSK to attack sukunas soul directly So either Gojo didn't wanna kill sukuna Or he opted out of using SSK for what ever reason Or he just cannot wield it So Yuki being able to use it is unlikely
Mind you gojo clearly has the best soul perception in the series up there with Mahito because he can distinctly see the soul
But seeing another's soul DOES NOT MATTER
You can hear other people's souls You can see them You can do what ever None of that gives you the ability to affect them
Yuji and Sukuna have the ability specificly Because they can see the shape of THEIR OWN SOUL And so far other than a special case like Mahito who's CT is based on the soul
That's the only way to become aware of the outline of your own soul
The second image shows that Sukuna wasn't aware of it until he Shared a body with Yuji
Mind you this is sukuna the guy that split his own soul into 20 fingers
And he wasn't aware of the outline of his soul until he shared a body with Yuji
The soul book only helped Yuji because he already had the ability to affect other people's souls
All it did was help him refine the ability to target the barrier between a incarnated sorcerers soul and the host
If the book allowed someone to affect souls All the heavy hitters would've read it before the Sukuna show down