Sukuna always gave me this impression where he's a pretty vanilla guy when it comes to sex. He's good on the bed, yes, but he'll just fuck you raw and toss you aside. Pretty basic sex until he met Yuuji. And it's not because Yuuji is a kinky sex pest but because Yuuji would do something or wear something and it'd instantaneously make Sukuna's dick bricked up. Yuuji, topless, raised his hands up to grab something from a shelf and Sukuna immediately develops an armpit kink. Yuuji wears his stirrup socks and Sukuna got a thing for thigh highs and feet now. Kinky weird unconditional fetishes Sukuna because Yuuji doing something is an instant kink/fetish for him.