After the death of her close friend Mari Hanashiro, Arisu Ichinokuro inherits Mari's Mushi (insect-like creatures that consume peoples' dreams and thoughts in return for supernatural powers), Morpho Butterfly. In order to find out the reason she was given her Mushi, Arisu sets out to find out more about Mushi and Mushitsuki with the aid of Daisuke "Kakkou" Kusuriya, an agent of the Special Environmental Conservation Executive Office assigned to be her bodyguard.