Sourin fights on the side of Ishida Mitsunari against the forces of Tokugawa Ieyasu alongside his retainer Tachibana Muneshige. He fights atop a large tank called "The Head of Xavi" which is created in the image of the late Pontiff Xavi. Cannonballs shoot out of its eyes, as well as sing a Xavi hymn.

He seems to be related to Xavi as you can see in a picture of him and Xavi on the bridges of memories.

(Source: Wikipedia)