The narrative of Mushi-uta is set in the near future. A decade prior to the story's beginning, peculiar insect-like entities called "Mushi" started to appear. These Mushi can consume people's dreams and thoughts, granting supernatural powers in exchange. By the conclusion of the first episode, the protagonist, Daisuke "Kakkou" Kusuriya, meets a young girl named Shiika Anmoto. Over time, the two grow quite close. Yet, unknown to Kakkou, Shiika is an escapee from a clandestine facility called GARDEN, which houses individuals possessed by Mushi, referred to as Mushitsuki. GARDEN's military arm, the Special Environmental Conservation Executive Office, sends its top assassin to hunt down Shiika. However, they encounter opposition from the Mushibane resistance group, commanded by the enigmatic "Ladybird."