Who is Kusami from Magician, Master and what is their importance?

Kusami is actually spelled Kasumi. Kasumi is Katsumi's youngest son. He is Tsurani, but he finds the war to be useless, and his father takes in Laurie and Pug so that they can teach Kasumi how to be a Midkemian. Kasumi brings the offer of peace to King Rodric.