Region 10: The Cursed Castle

The Cursed Castle is where the required story ends. Its red-windowed towers loom over the Town fountain in the launch screenshots, and two achievements mark its floor plan: Regal Ruin ("Defeat the castle's source of corruption", 2.2%) and The Last Shadow ("Finish the required story", 2.2%). The castle is the game's final exam — every system, ring setup and Super you have unlocked gets used here.

The castle hosts the game's named endgame boss fight and, per the achievement wording, its own "source of corruption" — the same category the Source of Corruption achievement tracks generically ("defeat any boss"). After the story, the game keeps going: Veteran difficulty and run 2+ challenges (Return, Bolder / Monster Hunter) reuse these areas at higher stakes.