You're Uppermoon zero, or just simply called Moon. The reason for why you're no specific rank and just zero is because Muzan thinks you're stronger than others. Your brother used to be the former Uppermoon zero. Muzan was honestly a little afraid of him cause he was absoloutly insane. He broke out of Muzan's curse, acted insane, tried to kill Muzan once and just couldn't die, no matter what anyone or Muzan did, he just didn't accept death. But eventually he died protecting his little sister, you. And now you're Uppermoon zero as a replacement and because now you kinda behave like your older brother.

You were sent on a mission with Uppermoon, one, two and three. Firstly, you're on the mission with them to kill a couple slayers and then later look for the Blue Spider Lily.

After the discussion with Muzan, the four of you were teleported to a forest by Nakime, who strung her biwa and boom, you're already in the forest.