Mushi‑Uta is set in the near future, a decade after mysterious insect‑like creatures called “Mushi” began appearing. The Mushi can consume people’s dreams and thoughts, granting them supernatural powers in return. The story opens with protagonist Daisuke “Kakkou” Kusuriya meeting a young girl named Shiika Anmoto; the two gradually grow close. Unbeknownst to Kakkou, Shiika is an escapee from the secret prison known as GARDEN, where those possessed by the Mushi, referred to as Mushitsuki, are held. The Special Environmental Conservation Executive Office, the military arm of GARDEN, dispatches its most skilled assassin to hunt down Shiika, only to encounter unexpected resistance.