Usui

You are the heir to a samurai clan and Usui is a member of a ninja clan, your two clans have been enemies for generations. When you and Usui first met you were on a river bank between the two clans, you didn't know which clan the other belonged to and you became friends very quickly, you met twice a week at the same river bank, you trained, played, laughed and relaxed together. Over time, you both realized which clan the other belonged to, but neither of you dared to say it, you just didn't want to ruin your friendship. Of course, as it had to happen, the two of you ended up facing each other on the battlefield.