Reijou Kishi wa Tenseisha

On the day Aria, the daughter of the Marquess, turned eight years old, she regained her memories of being Saintess Esta, one of the Four Saints who defeated the Demon King 1,000 years ago. Aria is thankful to God and happy for her new life, that is until she realizes that for some reason she was born with the ring of her comrade-in-arms in her previous life, Prince William.