Who is The Knights of the Cross - Michael, Shiro, Sanya from Death Masks and what is their importance?

The three Knights of the Cross are mysterious, powerful forces for good. Their swords, paranormal abilities and wisdom give them the strength and means to at least fight evil to a standstill. Michael is a frequent ally and collaborator of Harry's. Shiro is an elderly Asian samurai, whose sacrifice of himself to save Harry results not only in his own death, but in a powerful lesson for Harry about the transcendent power of both integrity and faith. Sanya is a new recruit, formerly possessed by a demon, who realized he had another, better choice about how to use his spirit and made it. He, like Shiro, provides a dynamic example of the value and power of positive, life-and-spirit affirming choices.