The narrative begins with a flashback to the garden of the Third Assault six years ago, where the young Riselia Ray Crystalia, also known as Selia, and her maid Regina discuss their hopes and dreams. The scene quickly turns dark as they learn that the Holy Knights, including Selia's family, have been defeated by the Voids.

Cut to the present: Selia, Regina, and Leonis Magnus, who now goes by Leo, arrive at the Seventh Assault Garden. Selia explains that the Assault Garden is a massive, mobile fortress developed to combat the Voids. Leo is introduced as a refugee with a Holy Sword, and Selia assures him that he will be accepted into the Excalibur Academy, a training facility for Holy Sword wielders.

During their tour of the academy, they encounter Musel Rhodes, an arrogant student who mocks Selia for not possessing a Holy Sword despite her lineage. Leo almost confronts Musel but is stopped by Elfiné Phillet, another member of Selia's squad. Elfiné informs them that she has detected strange magical reactions in the area, suggesting a possible Voids nest.

The trio heads to their dormitory, the Hraesvelgr Dormitory, which is older and less luxurious due to their squad's lower rank. Selia invites Leo to join their squad, emphasizing that the choice is his. While bathing, Leo accidentally reveals that he healed Selia not with the Holy Sword but through other means. He cryptically explains that the healed Selia is no longer the same, leaving her confused.

Meanwhile, Leo's demonic servants Blackus and Shary are tasked with investigating the military strength of the humans. Leo himself plans to infiltrate the academy to gather information while ensuring his basic needs are met.