The game begins with a brief recap regarding the events of Arle's life prior to her final exam, she talks about encountering Schezo, Satan, and how she came to meet Rulue and Minotauros. Like her other exams, Arle must journey through the dungeon and clear it in order to graduate. However, unlike the rest, this exam is being taken alongside other students including Lala and Rulue.
Deeper into the dungeon, Arle encounters her principal who forgot his mask, revealing himself to be Satan. She promptly fights him, only for Rulue to arrive once he's defeated and challenge Arle to another fight. Amidst the chaos, a new pathway reveals itself in the dungeon, a path that Satan was likely trying to seal. Arle decides to delve into this newfound path, called the Ancient Labyrinth, and finds inscribed plates which she can't read.
While journeying through this part of the dungeon, she finds a bracelet that allows her to read the writing on the plates. However, the bracelet belongs to Schezo who somehow made his way into the Ancient Labyrinth. After their typical exchange, Arle and Schezo battle, but she heals him afterwards in order to gain information about this labyrinth connected to the principal's dungeon. Schezo explains that the ruins contain treasures with powers of interdimensional scale. Arle thanks him and attempts to return the bracelet, but he says she should keep it as she's earned it by defeating him. Shortly after, Arle and Rulue meet again with the latter challenging Arle to a rematch.
While exploring the dungeon, Arle discovers that the treasures are protected by four guardians who must be pursued. Rulue once again catches up with Arle, but they're interrupted by a commotion-- Schezo had broken a seal while doing his own exploration and encountered the treasure guardian Phantom God.
The three team up to fight Phantom God, but he proves to be too powerful. He prepares to kill all three, but Schezo quickly creates a void for Rulue and Arle to escape into, sacrificing himself in the process as Phantom God strikes him down with thunder magic.
Arle awakens in the dimension Schezo prepared, the Phantom Zone. While exploring, she encounters a woman with a striking resemblance to her. As she's unable to explain the resemblance, Arle concludes that she is a doppelganger. Arle's mysterious doppelganger makes a bet with Arle: if Arle can find her enough times, she'll grant Arle the necessary tools to defeat Phantom God. Arle accepts and succeeds, her doppelganger giving her some key advice before ejecting her from the Phantom Zone. She ends up in the Guardian's Floor where she seeks out the four treasure guardians: Red Ruby, Yellow Diamond, Blue Sapphire, and Green Emerald who grant her the Ruler's Mantle upon defeat.
Arle returns to challenge Phantom God once more and defeats him with her newfound strength and equipment, and obtains the Seraphim Orb, a powerful artifact. Phantom God informs her that he never truly killed Schezo, but merely teleported him outside of the dungeon and erased his memories to prevent him from acquiring the Seraphim Orb. Arle uses the orb to erase her and Rulue's memories of the incident since she decides keeping the Seraphim Orb's existence a secret is important. She continues on with her final exam after this point.
