The Cathedral is described as a place with a very high ceiling, a skylight, golden ornaments and white stonework. There are also windows, but it is unclear where exactly they open to. Balconies adorn the front, left and right sides of the Cathedral, with the center balcony featuring a throne for the Game Master to sit on. During the trial, a series of benches is present for the human pieces to sit in.
The Game Master Lambdadelta uses the Cathedral to host the Great Court of Illusions, with Bernkastel and Erika claiming that Natsuhi Ushiromiya is the culprit while Beatrice's piece version and Battler defend her.
Though Battler is defeated, in the ??? he comes up with a new theory and battles Erika again to prove Natsuhi's innocence.
The Cathedral is redecorated to host a wedding between Erika and a comatose BATTLER. At the climax, the newly-revived Beatrice crashes the wedding and engages Erika in a duel.