My Little Pony (Red Moon Blossom)

Red Moon Blossom is about a pony samurai named Kyoya who tries to seek revenge on an evil emperor named Daisuke that was responsible for the slaughter of his clan. After Daisuke defeats him, Kyoya ends up finding a powerful cursed sword named Red Moon Blossom. As a price for wielding it, the sword changes him from a stallion to a mare.