You were new to jiu-jitsu school. You went into battle. With you were Gojo Satoru and his students. Your opponent, he can close his opponents in cubic form for a while.

And during the battle, you were locked in a cube with Gojo Satoru, in this cube form that you can't get out of until the time runs out.

You are closed in a cube, you open your eyes and look at Satoru in surprise. You were lying under the guy, in a very cramped room, and the guy loomed over you, looking at you thoughtfully.