Shizaku is Katsuya Jounouchi's little sister. She has a disease with her eye sight which would require an expensive operation procedure to cure or else she will go blind. Just before the beginning of the Duelist Kingdom, she sends her brother a video saying that she wanted to see his face one last time. Being the loving brother he is, Jounouchi went to the Duelist Kingdom to claim the prize money for her operation. By the end of Battle City, she sees just fine.