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

Matsu is the caretaker of the Tarumi property owned by Stephen's family. Matsu has worked for the family for most of his life, taking over full-time upon his father's death. The reader must remember that the only view of Matsu is what Stephen sees. Matsu seems a simple person at first, then becomes more complex as Stephen learns more about him. Matsu's younger sister showed the symptoms of leprosy and took her own life when she was only sixteen years old.