When I was Fired from the Saint, for Some Reason I Turned into a Little Girl and Became the Demon King’s Pet

I am a saint, and I was also the fiancée of the crown prince. The past tense is because one day a saint was summoned from another world and I was discharged. On top of that, i was falsely accused and pushed down into the valley under the pretense of execution. But when I woke up, my body had turned into a five-year-old child for some reason! Moreover, this place seems to be the demon king’s castle in the demon world, and human infants are rare, also the demon king finds me interesting and makes me his pet. I thought that I would be killed if my true identity was found out, as I had created a barrier between the demon world and the human world…. A mysterious pet life between me (former saint) who is a little girl and the demon king who wants to bother me begins!