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".
This song is an arrangement of "Kokoro・Kiseki" which tells why Rin, a genius "chemist", developed "Lambda Organ". When Rin was born, her body was in stitches. She was able to be born alive, while her twin brother couldn't. But she had to stay in a biological clean laboratory alone all her life. Since she had lived in loneliness, she wished her brother had been with her. So she developed "Lambda Organ" (KAITO). Knowing her time to live was short, Rin sacrifices her own heart to awaken Kaito.
This is a parody arrangement of "Kokoro. Rin was a genius "chemist" who developed "Lambda Organ", a nameless "creature" (KAITO). But it was still missing "kokoro" and it wished to know what is like to have it. After a few hundreds years, the Lambda Organ is found only to end in disaster, as the experiment in an attempt to get his own heart, begins to assimilate all the living creatures along with their memories, transforming the planet in wasteland...
This is an arrangement of both "Kokoro" and "Kokoro・Kiseki" which tells of an alternative future for the "Lambda Organ". After Kaito is awakened, he finally realizes why he was born and sends a message to the past for Rin. Final, they are reunited and spend their last moments of life together.