Hake is the Inukami of the head of the family who gives out most of the missions for the other members of the Kawahira family.
He made a contract with the head of the family when she was near Keita's age on a Non-contract day (coincidently her birthday fifty years before the start of the series), which he claims was because he was bored with his eternal, uneventful life.
The contract item he was given are the decorative beads he wears. Also, there is evidence that his weakness are fleas.