Princess Knight(1999)

In heaven, boys and girls were assigned their gender by being given a blue heart for boys and a red heart for girls. One of the cherubs does not want to stop being a cherub, so he gives one of the girls (Zafiro) his blue heart, because of Cachito's mischief, who is sent to earth as punishment to correct his mistake. The story really begins when, after a few years, the elf-like angel finds the girl and tries to convince her to return the extra blue heart he gave her. At birth, her situation is already complicated: in her kingdom, the Salic law prevails, so the king passes his baby girl off as a boy to prevent unscrupulous nobles from seizing power.