The pug had been a replacement, though the pug did not know this. He was well aware that the rest of the pack was much older and far more experienced than him, but he never gave it much thought. He was still a pup after all, was still able to enjoy all the extra attention he received without questioning it. He loved that most of the training-sessions seemed to revolve around him, loved that his master seemed to care for him the most, would go so far as to let the pug stay at his house, even when the other dogs of the pack were long dismissed.
His master had his own pup, a little boy of two years, and when ever the pug had some time at paw he would spent it with the boy – playing, rolling around and remembering that they both were just kids. For this the pug soon understood: While his master was a kind and loving man, was a good master and a good father, most of all he was a shinobi through and through and did not know how to be anything else. When he had taught his boy how to walk, the walking wouldn't stop where the horizontal ended, instead of nursery-rhymes he taught him basic jutsu and where other parents showed their children how to hold a pen, he showed his son how to hold a kunai. Not because he intended to turn him into an efficient tool for the village as soon as possible, but because he simply didn't know any better.
The pug never wondered if this was right or wrong and the boy seemed to enjoy it – as with all little boys, anything that brought him closer to the almightiness of his father was highly appreciated – yet they both enjoyed every minute they spent together playing games that served only one purpose, to be a game and not to train. Not surprisingly, the boy's name was the first human word the pug learned.

After two years the pug was no longer a pup, well trained and old enough to follow his master and pack out on missions. Thus he found nothing strange in it, when in the same year the boy was send to the Academy. Because they were both grown up now.
How wrong he was with this the pug learned later. The boy had graduated, had passed his chunin-exam and was finally send out on missions that involved much more than fixing some peasant's roof.
One night he came home from a mission, six years old, covered in blood, wide eyed and shaking.
He wasn't injured. But he had learned something that day. He had learned that while in theory, when you kill someone they died – which wasn't the most pleasant idea, but something unavoidable when killing someone – in practice they also screamed, and bled and possibly lost a whole lot of other body fluids and they looked at you, even if they could not possibly see you, they still looked at you...
His father did not understand or he understood too good. (There are things you can only understand, if you don't understand them at all.) He took the boy to the bathroom and helped him out of his blood-soaked clothes. He taught him that first you washed your hands, then your hair and then worked your way down, taught him that you must never forget to clean your nails and clean them good – because there was always some blood stuck underneath and even if you could not see it, the faint smell was enough to drive you mad. The boy nodded stoically, listened to every word his father told him. He did not cry, did not throw up – even though his father said it would be perfectly fine after your first kill.
The pug watched from the hallway, watched as his master brought the boy to bed where he left him alone. He watched through the door, which the father had left ajar, as the boy curled up under his blanket, and – once he believed he was truly and fully alone – started to cry.
It was then that the pug realised that while he was by now a fully grown dog, the boy was still a boy.
The pug slipped through the crack in the door and boldly jumped on the boy's bed, where he lay down next to him and soon felt one little hand wrapped around him, one little forehead rest against his back and tears wet his fur.

When, after the Iwa-incident, his master resolved to rather end his life than live on in shame – when he told his dogs about this decision, it was the pug and no one else, who spoke up.
Of course the rest of the pack did not like their master's plan either, but they figured that they could not understand such human concepts and problems. It was the pug who reminded his master that he was not only a shinobi, but also a father and that he should think of his son.
"He'll understand", was all his master said "He's strong. He'll deal with it."

There wasn't a real funeral, but after the small ceremony the pug sought out the boy – who sat in his room, motionless, two dark and dead eyes fixed on the wall. The pug believed that the boy needed someone to comfort him, but the second he neared him, the boy leaped at him with all the rage of a confused and angry and lost little boy trained to be a killing-machine.
It was the ninken's fault. The canine loyalty, the way of the pack that was to blame for his father's fall.
He just needed some time, the pug thought.
He gave him time, but months passed and the boy did not stop blaming the dogs.
In the end the pug gave up, left the boy alone. Maybe this was how it was, and there was nothing he could do about it. Maybe the other ninken had been right when they told him not to meddle with humans too much – because there was no way to understand the strange ways in which they worked.
For years the pug heard nothing from the boy. He sometimes worried about him, especially when he heard that war was declared between Konohagakure and Iwagakure. He sometimes considered to see how the boy was. But he never did. He waited.
If, one day, he would come to his senses, the pug would be there, he would let the boy summon him and he would help him to build up his own pack of ninken, would teach him how to train and to work with them. He would forgive him. But it was the boy who had to make the first step.

After the war had ended, the pug had almost lost hope. Part of him had settled with the grim belief that the boy had died, when one day he was pulled from the meadow where he had just been chasing some bitch, and into a small, shabby apartment.
The boy, the pug had to admit, was no longer a boy. He wasn't quite a man yet either, but he was teen enough not to be called a child any more (though he hadn't been called that for a long time).
He sat in his bed, cross-legged and stared at the pug with his right eye. His left eye scarred and squeezed shut.
The pug stared back.
At last the boy turned his head, looked away and held out his hand.
The pug understood. He sniffed at the boys fingers, then – the boy was still looking away – leaned his head against the boy's hand, before he dropped to the mattress, where the boy soon curled up next to him, wrapped one not so little hand around the pug's body, rested one almost fully grown forehead against the pug's back and allowed his tears be soaked up by short, brown fur.
The pug never asked what had happened, he gathered bits and pieces of information that gave him an idea of the story. But he kept his promise. He helped the boy to find his own pack of ninken, taught him how to train and to work with them. It was only natural that he ended up as the new pack's alpha – not only was he the oldest and most experienced among them. He was also their master's closest and most trusted friend.