He is known to be stubborn and distrustful of other dogs but really caring towards his own dogs.
Eijirō is the leader of the neighbor pack.
When humans attack his territory, he tries to escape with his minions but cannot find his mate nor puppies. He attacks Tomon at first, believing him to be a hunting dog. Tomon tells him that his family is safe in his territory and that he should go there along with his minions. Eijirō is distrustful of Tomon, telling him that he will kill him if it turns out to be a trap, but does what he said.
It can be assumed that Eijirō happily reunited with his family in Tomon's territory and they moved back to their own territory after humans left.