From the introduction:
The date is January 2nd, and the year is 2100. Yesterday in the nation of Japan, three scientists conducted an experiment. Yuki Terumi, Relius Clover, and Shūichirō Ayatsuki. They attempted to bypass the Boundary and reach into the Blue. Or, since those words likely mean nothing to you, allow me to simplify them. They attempted to reach into another dimension, most likely the afterlife, and gain access to the spiritual battery that governs the cycle of reincarnation.