There is no actual relationship between Hero and Don John. Hero's father is a good friend of Don Pedro, Don John's half brother. Hero is like a daughter to Don Pedro and he cares for her and her family. Don John hate Don Pedro and wants to get revenge on him for defeating him. He schemes to do so by humiliating Don Pedro's dearest friend, Claudio. Claudio is in love with Hero so she gets caught up in Don John's plans by association. Don John couldn't care less what happens to Hero and she really has no direct ties or communication with Don John. She is simply the tragic victim of his plans to hurt his brother.