The world we live in has dangers that most human beings have never experienced. Dangers that are too lethal to be allowed to run free. Shadows. That is where the Sentinel Society comes in, a secret ancient organization with the sole focus to protect mankind from the Shadows. All the sentinels are bound by rules, rules that they must uphold till their last breath. That was until Yasu Endo met Kai Kagami, a boy with the power to control the shadows themselves!