A track composed by Vocaloid producer Tsuru. Opening with an evocative arpeggio and featuring an expressive guitar solo in the interlude, the song combines emotionally stirring guitar sounds with Michitose's delicate yet sincere vocals, powerfully conveying her feelings to the listener. The title "Petrica" is a coined word combining "petrichor", the scent that rises when rain falls, and "eureka," an ancient Greek word meaning "I found it!" It is a song that symbolizes the world of the EP Fushigigaru.