A mysterious moon spirit who showed up in episode 24 with some undefined connection to Michiru. The name "Muu" is basically derived from "Moon" (ムーン). He's got this quirk where he ends sentences with "mupu." There's also this incident where Kaoru rescued both Moop and Hoop after they got trapped under a fallen tree.
Content compiled by AnimeList.moe from publicly available sources.
