One year after the Sanctuary's events, Subaru Natsuki trains to face future challenges. Peace is shattered when Emilia receives an invitation from rival Anastasia Hoshin to meet in the Watergate City of Priestella. Concerned for her safety, Subaru and his friends accompany her. In Priestella, Subaru reconnects with old allies, but new, dangerous foes emerge. Driven by fanatical motives and ruthless tactics, these enemies target Emilia and threaten the city's existence. Subaru must rally his allies and give everything to stop their destructive goals, ensuring the safety of Emilia and the future of the city from impending chaos.