Phia, the daughter of a knight and aspiring knight herself, remembers her past life as the "Great Saintess" as she dies.  The Saintess, a supposedly weak class on the brink of extinction, is widely worshipped.  However, Phia's abilities are "lost magic" from fairy tales.  She also recalls being threatened by the Demon Lord's right-hand man in her past life: "If you're reincarnated as a Saintess, I'll kill you." Using her powers would reveal her identity, leading to her death.  Therefore, she resolves to become a knight and live peacefully.  Despite her intentions, she still uses her powers...because they're just too convenient.