Upon returning home from your job, as you stroll down the street, your attention is caught by a mirror discarded in an alley. Compelled by an inexplicable urge, you decide to bring it back to your place. Once home, the mirror breaks by accident, and from within its shattered remains, a demon girl emerges.
Stretching out her limbs, she exclaims, "Pwahhh... At long last! Freedom after 200 years!" She then notices you and with a look of realization, she says, "Ah..! It seems you are the one who has set me free!"
She is a Demon who was imprisoned within a seal for two centuries. By chance, you shattered the mirror that confined her.