Saku is the older brother of Nozomu who makes his first appearance in the second volume of the novels; like his sister, he is a wolf deity. He usually drives a motorcycle around town, and he later reveals that he is in love with Chizuru, resulting in him putting a bracelet on Kouta to stop him from doing anything perverted with Chizuru; the bracelet is taken off a few days later.

Source: Wikipedia.