The Kokoro Series was created and produced by Suginohito and his group, who changed the original lyrics of the song Kokoro, and based it on a fanfic written by Oshimaino-P. The Kokoro series is a trilogy of songs with a slightly humorous yet sad tale. In a similar fashion to "Kokoro" and "Kokoro・Kiseki", a lonely scientist creates an artificial creature. The series has two endings, with a comical "Bad End" route and an emotive "Good End".