The sudden appearance of a “Mushi” in front of Ichinokuro Arisu happened immediately after the death of her close friend Hanashiro Mari. In addition to following Arisu closely, the four antennae silver-colored Morpho butterfly would sometimes transform into a variant long lance to protect her. Why is that? Together with Kusuriya Daisuke, a teenage boy who was sent by a top secret agency “The Special Environmental Preservation Bureau” to monitor over her as a “Mushitsuki”, Arisu began her search for the answer.

Engraved eternally by the shining sliver-lance,

This is the highest and the worst girl meets girl!