Cerberos

Hiruma's ferocious dog, Cerberus is named after the Greek mythical creature that guards the gates to Hades. Though incredibly intelligent for a dog, Cerberus is apparently driven entirely by his appetite. Hiruma often uses Cerberus to frighten his players into training harder, and also to track down missing club members. However, in one omake Q&A segment, the Devil Bat claims that Cerberus is a wild dog that simply stays with Hiruma in order to get food more easily.

In the anime, it was shown that Cerberus simply showed up at Deimon's football field when Hiruma was in middle school. Hiruma noted that Cerberus had "a good look in his eyes" and challenged the dog to a showdown. When they clashed, Cerberus managed to tear one of Hiruma's sleeves, but Hiruma had fastened the spiked collar on Cerberus in an instant, making Cerberus the loser. According to Kurita, Hiruma took a liking to Cerberus, and Cerberus did everything Hiruma told him to (and showing in episode 27 that Hiruma really did care for Cerberus a lot).

Cerberus is somewhat anthropomorphic, and is able to use his front paws like hands while standing on his hind paws and talk. According to chapter 251 of the manga, Cerberus can bench press 120kgs (264 lbs).