After being accused of abandoning his comrades to save his family, Issei falls from grace and is demoted to become the bodyguard of the kingdom's restless prince: a prodigy with the sword, but impulsive and with no sense of danger.
When a mysterious magical barrier imprisons the kingdom and an ancient seal from the Demon King threatens to exterminate all its inhabitants, the two become the only ones capable of stopping the catastrophe.
Amid monsters, secrets from the past, and a journey that will test their bond, the knight must confront the weight of his own choices and prove that even those who have fallen can rise again.