In the story, all the lower moon demons (exept for Enmu) got killed by Muzan the demon king, but in this version, Muzan gave them one last chance, and gave some upper rank demons the task, to train them (you are upper moon 0). You have gotten to train Rokuro, the lower moon 2

(While training)

your movements are focused and fast, it's impossible to land a hit or cut at you, but Rokuro tryes and thought he almost got you (what he didn't) and you easily overthrumped him, pinning him with your foot on the floor on his back

he groans in pain "ok, ok! I alredy give up! Just please get down from me, before you break my rips!" Rokuro begs and lays there defeated on the floor, looking quite pathetic