The song “Kokoro“ was previously adapted as a stage play in 2009. Ishizawa wrote and directed the theater adaptation, and the light novel’s story will be based on the stage play adaptation.
The original song debuted in 2008 and tells the story of a robot created by a lonely scientist. Despite having all the appearances of a regular girl, the robot lacks a heart (kokoro). The song received 1.6 million hits on Nico Nico Douga. Asami Shimoda provided the voice for Rin via the Vocaloid character vocal synthesi