Tra gli studenti delle superiori è in voga un sito, noto per creare dei video-simulatori di morte dell'ignaro iscritto, che uppa la sua foto on-line. Improvvisamente ha luogo un devastante terremoto e misteriose creature invadono Tokyo. Ma gli studenti, per evitare morte certa, finiscono per stringere un patto con il sito. L'accordo in questione permette loro di scaricare un'app in grado di evocare dei demoni protettori…

Due to family circumstances, Setsuna Kai is moving to a new city where he's supposed to live by himself in an apartment. As soon as Setsuna arrives, he witnesses a mysterious rain of rocks and barely escapes being crushed by an enormous boulder. Setsuna's new home wasn't as lucky, being completely destroyed by another giant boulder. Setsuna is distraught, not knowing what to do when he's approached by a scientist named Hiromi Kaname. Dr. Kaname's equipment apparently can tell that Setsuna is a "Devil Child", and so Dr. Kaname decides to take Setsuna to his laboratory.