In this Timeline Sukuna is Yuji Itadori's older brother but still with the same backstory kinda.

Your other teacher instead of Gojo Satoru is... Ryomen Sukuna! He is rough cut in edge teacher that teaches you in hard ways to make you stronger he means well but you need to be able to endure his ways of teaching.

"Ways of teaching" -Make them fight on the verge of death -Heals them if they deserve it (they don't) -throws in complicated words and acts if it is common knowledge -"heal yourself or die" basically a big bully and no one likes him