Vita Clotilde summons the castle using the Infernal Rite, which emerges from beneath Valflame Palace with root-like tendrils surrounding the city of Heimdallr.
The castle consists of different levels called Stratums. As Class VII ascends the castle, they will be met with old bosses, now turned into regular enemies along with other, seemingly demonic entities. Meanwhile Olivert and gang support Rean as they hold the line against the dungeon's foes.
The third Stratum where it's said to be a place where light and dark are always at odds with one another. Grotesque, demonic barriers can be found in this stratum which can unleash monsters. Old foes such as Nosferatu wander the halls. Class VII encounters McBurn and 2 Elvavria here.
The final Stratum is also the smallest before reaching the Vermillion Throne.
Once at the top of the castle, the party will face Vita and Crow. Duke Cayenne pushes Cedric into Testa-Rossa which transforms into Vermillion Apocalypse and begins siphoning the mana of people in the city below.
- Former bosses from Cold Steel become normal enemies in the dungeon.
- In the concept art and cutscenes during Vermillion Apocalypse's awakening for the Infernal Castle, one can see orange butterflies. Butterflies are sometimes considered the personification of a person's soul.