It was funny how Giyu cut Rui's head in that instant he blinked xD Not sure why the anime skipped the explanation, but in the manga the narrator said that the Eleventh Form is something created by and can only be used by Giyu
Florin
2019-12-04 12:05:33 +0000 UTC
Rui said he cut off his own head with his threads before Tanjiro could. Rui wasn't even going all out during his fight with Tanjiro. He definitely has a long way to go.