What kind of stance is this?

This is chapter 17's cover. Gojo training yuji with the help of one of yaga's puppets.

And they are both (yuji and gojo) assuming this position which i find strange, because it felt uncomfortable when i tried it.

In case you can't see it, the left hand's palm is facing away while the arm is extended.

I am not a martial art's specialist, but i don't know what advantage would be gained from such a position, at the same time i assume gege did his research.

Do you know about this? Please do tell