Once a normal high school boy, Hyde was attacked by the Void. However, thanks to the help of a mysterious young girl named Linne, he was able to barely escape death. Upon discovering that the attack had turned him into an In-Birth, a being that can utilize EXS, he is forced by Linne to fight alongside her against the threat of the Void.
Linne has since claimed respite in Hyde's house, much to the latter's chagrin. After fighting countless battles together as part of "special training", Hyde has become accustomed to his powers. He relies greatly on Danretsu no Menzaifu, the sword that Linne entrusted to him. During this time, he has also met the gargantuan brute Waldstein, who also happens to be Linne's comrade.
But when the phenomenon known as the Under Night suddenly appears, Linne and Waldstein mysteriously disappear, leaving only a message for Hyde to stay away.But he will have none of that. Hyde vows to find Linne and Waldstein, and settle a score with the mysterious woman known as "Paradox"....
He wakes up -- In order to free the girl from the chains of eternity that seal her fate. The