Players seeking the Backstreet Courtyard Key in Phantom Blade Zero will find it is not related to Old Man Gen's house or the third acolyte scarecrow as one might initially assume. Instead, this key becomes accessible later in the game, specifically within the Mountain of Imprisonment area.
Those who have been searching for the key with the intention of unlocking the inaccessible area near Old Man Gen's house will need to acquire the Flaming Mane phantom edge from the region boss. After obtaining it, players must follow the main quest to repair the edge with Lei Dang. This repaired edge can then be used to burn away a barrier located by the Pond of Fading Song bell, where Gu Wanyue, The Wailing Wraith, was fought. This path provides access to both of those quest locations.
To obtain the Backstreet Courtyard Key itself, players must progress to the Mountain of Imprisonment. There, they should speak with the couple situated near the Shrine Outer Gate. Following this, the Ledger of Atonement quest must be completed by locating the ledger within the caves situated below. Upon returning to the woman at the shrine, players can initiate the Bai Xue quest, which rewards them with the Backstreet Courtyard Key. This key's primary relevance is to this specific questline, and it holds little other value in the game.
Access to the Mountain of Imprisonment requires the prior completion of the Illusory Pipa quest. The Backstreet Courtyard Key is used to open a locked door in the backstreets of Pangzhen as part of this quest progression.