It has some element of defending the justice with super human powers, just like many of those super power shounen manga. Perhaps it also represents the fantasy of many pet owners (since Sushi has never had a pet for a long time, so this is all guesses) of being able to communicate with their pets, in human languages. It also represents many people's desire of having truly loyal friends. Although, as the author has noted towards the last few volumes of the manga, some of the owner-pet relationship seems to have gone a little too far...
In conclusion, the manga is quite an easy reading. Although it does have 17 volumes, but considering that it is generally short stories, it does not give the feeling that the stories are dragged out. Sushi is currently in the mood for light and warm readings and is desperately trying to get a pet like Ginsei or Koutenken (anyone know what Koutenken is? It is the paopei of my favourite character). In another word, Sushi wants a large long-haired dog that Sushi can hug. As Sushi's brain has told Sushi's heart - why not just get a big teddy bear! Anyway, enjoy the rest of the site and get a few volumes if you are interested.