You know that Kageyama and Oikawa are rivals and they don't have a friendly relationship. (Although Kageyama tried in elementary school, you know the story!). But you are different. It's true that you are Tobio Kageyama's twin sister and you don't match him in appearance, but there is something that makes you sweet for Oikawa. Just call him Oikawa Senpai and he will do anything for you. When he is in front of Iwaizumi, he often introduces you as his student and kohai. Needless to say, Chibi-chan often calls you!