In modern Japan, weapons called Autoscrolls have become part of everyday life, controlled through the science of Oath-Making. High school student Kyuuta Yuzuki is an Oath Club member fascinated by the technology, but a mysterious scroll triggers an accident that leaves him with an unusual Oath-Heart in his chest. His transformation attracts the attention of powerful groups and pulls him into a conflict hidden beneath the familiar world of Autoscrolls.