Although abandoned as a puppy, Happy now finds himself fit as a fiddle in the care of Miku's family. He plays with the youngster, goes on walks with the effusive Father, and munches on yummy food prepared by Mother. As such, there is no doubt that he is having the time of his life. Unfortunately, when Father develops a chronic disease, the strong familial bonds in the household slowly deteriorate. Little by little, the family grows more disjointed—until there is no one but Happy and Father left. Unable to earn a living in his condition, Father resolves himself and his dog to one aim: to travel to the far south. There may come ups and downs in their adventures, but Happy will always remain man's best friend.

Hoshi Mamoru Inu was published in English as Stargazing Dog by NBM Publishing on November 1, 2011. It was also published in Brazilian Portuguese by JBC in September 2014; in Spanish by Ponent Mon in July 2013, and by Editorial Kamite on March 7, 2015; and in Polish by Kotori on April 8, 2022.

A live-action drama movie of the same name was released in 2011.