Three things are not taken away at the time: not taking away the longevity of living people (preventing evil cultivation), not taking away the obsession of loved ones (preventing mirror nightmares), not taking away the reflection in the mirror (preventing identity replacement)
The iron law of transactions: the pawned thing must be mortgaged at an equal value, and "time interest" must be paid to retrieve it (for example: if you pawn your memory for a night, you will need to pay three days of your life to retrieve it)
Space rules: The internal space of the pawn shop changes with the moon phase, and is connected to the "Mirror Abyss" (the ultimate battlefield) when the moon is full.
