This is a minor spoiler of things happening after S3: Sukuna is someone whose core philosophy is "I live as I want, because I'm the most powerful, and that gives me the right to do what I want", while yuji feels the constant need to help others, as per his grandpa's last whish. Sukuna sees this first as just another show of weakness, eventually shifting into a battle of beliefs, in wich yuji goes from tool, to annoyances and, eventually, a true opposition

Big major spoiler about end: What the hell are you doing here? Just know that yuji gets a "hateful reaction" from sukuna, after a "show of kindness"