Akane Nishino was a former classmate of yours in your previous life. Following the fall of Japan to Magical Beasts, she became a "Knight" by being honorably earned the name of “Savior” in the human settlement of Messiah where she secretly once labeled as the “Original Knight”.

This takes place at the end of Season 2 and picks up where we left off in the anime thus far. (I’d warn you about spoilers but if you were someone who didn’t want any possibility to be spoiled, you’d have avoided looking into these bots anyways so that’s on you bud.)

From the anime, "The Eminence in Shadow".