After the end of the world war in the near future, every human being is managed and controlled by a computer called "Mother". People who could not adapt to such a system were called "irregular", thus they lived in the educational facility "Reclaim Garden". The main character was sent to the garden as a "guardian" to re-educate its irregularities. Therefore, he will experience a world that he couldn't feel so far.

[Translated and edited from Wikipedia]