Everyone knows to stay away from Gaara.
If you cross Gaara, he'll put you in a living hell. No matter who you are. Even if you're supposed to be his brother.
Everyone knows that.
Nobody calls Kankurou by name any more. They always call him 'the Kazekage's son,' or, 'that poor boy.' It doesn't matter. After Gaara got done with the boy, Kankurou didn't know his own name. According to the medical nin, his mind was on the verge of a complete breakdown that would have turned him into nothing but a slack-jawed shell of a human being, muttering to himself in gibberish. So, in order to keep himself sane, his mind kind of did a system-restart: all of his memories, thoughts, knowledge, all the people he knew, every kill he'd made, every jutsu he'd ever learned, all gone. All that remained were basic systems and a question: Who am I? The Kazekage's son was placed in the care of his sister, or rather, the girl who used to be his sister. He couldn't remember, and she never spoke a word to him. She was half-ashamed, half-afraid of what had happened to him.
Things continued on as they always had for a few months, untill word reached the Sand that the Chunin exams were to be held in the Leaf, and soon. Well, the Kazekage had been acting a little strange lately, and formed a plan to join with the Sound and invade the Leaf. No one thought twice about it; after all, even if their leader was a bit... screwed up in the head, he was still their leader and they followed him without question. Those who didn't... Got a visit from Gaara.
But something strange happened when the two 'siblings' set out for the exams that were doomed to be interrupted. Upon tripping over some object in that poor boy's old room (she was in there to get a scroll, but found she must have moved it to her room), she discovered two things: One, the object tripped over happened to be the ugly puppet she'd aways despised, and two, as Karasu let out an irritated yell and then swore...
The puppet had somehow retained a portion of its owner's soul.
After being carefully studied by Chiyo, the old woman, it became known that the puppet could stand-in for the Kazekage's son, not only in battle, but in everything. Apparently, using the body-switch jutsu normally didn't have adverse effects, but Karasu was not a normal puppet. Sasori, the former puppet master, had performed many experiments on it, which had led to the strange ability to absorb a sliver of the user's life force every time the jutsu was used on it.
And so, Karasu became part of the plan. It was a simple matter to disguise one of the older puppets, Kuroari, as Karasu. Even simpler to disguise the latter as the boy.
The three 'siblings' from the Sand were back.
Temari was both frightened and annoyed by the new addition.
Gaara held it in indifference. This was not his old toy, just a fake used for deception.
And so, the Chunin exams began, and it became abundantly clear that Karasu was so good at being the poor boy, that it even lost, backed down, and made mistakes when it deemed necessary. An almost perfect copy. Not many people could tell the difference. It was as if the Kazekage's son was truly back.
But everyone knew there was no coming back for the true Kankurou.