Ginro

The Sumimura family's demon dog; he detects ayakashi with his sense of smell. He is about 500 years old. Madarao was previously known by the name of Ginro and was at one time friends with Koya. He currently wears a collar that seals away his true demon form. When unsealed, Madarao is a competent poison user and avid illusionist.

(Source: Wikipedia)