How would you explain yujis domain expansion?

it only shows up right at the end of the manga, in the Sukuna fight, and it's nothing like the flashy lethal ones. the space looks like an ordinary place out of his own memories rather than a temple or a void. the point isn't to kill anyone. the sure-hit is what lets his strikes land on Sukuna's soul so he can pry Megumi loose, which fits where his character ends up, since late in the story his whole thing is understanding souls. if I had to explain it in one line: a domain built to rescue someone, not to win.