help with the title

does anybody know the title of this?
there are many princes and our mc is one however he is originally a girl but she got rid of her chest so she got scars there. there’s a concept of disciple and masters and she trained at a very young age. there’s this battle that comes every 1000(?) years and it’s happening currently when i was reading it. it seems like the crown prince (? the child of emperor) likes her and her retainer. plz plz