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"No one can understand you as much as I can. You and I are one. You are my vessel."

In where Sukuna makes it his mission to make Yuuji dependant on only him. After any other human whether it be a civilian or sorcerer, will never understand what he feels.

Sukuna takes advantage of those moments of weakness to slowly break Yuuji's mind and heart. To make Yuuji give up his everything for Sukuna.