Where to find the Backstreet Courtyard Key in Phantom Blade Zero

I spent a long time in Phantom Blade Zero searching for the Backstreet Courtyard Key, convinced it would unlock the inaccessible area where Old Man Gen's house is located, as well as the third acolyte scarecrow. Turns out, that gate doesn't lead to either.

If you're searching for that key with that in mind, you instead need to acquire the Flaming Mane phantom edge from the region boss and follow the ...