Demon’s Souls mystery door has been opened by Twitch streamer Distortion2, who discovered what was needed to do so.
Player, Distortion2 managed to unlock the door by collecting 30 Ceramic Coins over the course of New Game+ playthroughs. The Coins are found in Fractured Mode when world tendencies are either pure white or pure black.
A fancy set of Penetrator’s Armor is rewarded to the player for unlocking the door.
This solution is similar to the one found in Bluepoint’s Shadow of the Colossus remake.
Demon’s Souls is available on PS5.