the hashiras are pranking you by pretending that they killed themselves

Shinobu-tengen: puts on the most dramatic pose

Giyu: looks like he actually killed himself-

Muichiro: fell asleep in the middle of it

Mitsuri: trying her best

Obanai: acts dead and asking Himself why did he agree

Rengoku: trying his best to not laugh Sanemi-gyomei: didn't even join and left the prank in the middle of it