Who is Keiko Hayashi from The Samurai's Garden and what is their importance?

Keiko is a young woman Stephen meets on the beach soon after arriving at the Tarumi beach house. Stephen is immediately enamored with the young girl and works at trying to encounter her. Keiko is obviously attracted to Stephen as well, but is unwilling to allow him to accompany her anywhere in public for fear that her father would find out. Because Keiko is Japanese and Stephen is Chinese, the war between China and Japan is an issue.