Kankuro has seen Gaara smile three times. One a 'slasher smile', one a smirk, and one that he never expected Gaara to give in his wildest dreams. SandSibs.
I don't own Naruto.
When Kankuro first sees Gaara smirk, at the sand shinobi stupid enough to try and assassinate him, it is a bit surprising as Gaara isn't one to show his emotions. He is usually introverted, and so the upturn of his brother's lips is unusual. A smirk on any other face would not be a cause for concern, in fact, Kankuro has come to find it is almost always accompanied by an opponent too sure of himself, but he distinctly knows that Gaara isn't one to be underestimated.
The glint in his eyes as the shinobi shakes in fear as sand slowly climbs over his clothes, and slinks up the cloth slowly as if not to waste unneeded energy, is what truly makes the expression morph from almost unremarkable to completely terrifying. Gaara watches the sand crawl over the body of the sand shinobi, who is either too proud to beg for mercy or too frightened to even open his mouth, waiting for the moment to crush the man in sand and drown his body in blood.
The sand shinobi trembles, and the sand covering him in turn makes little 'shh' 'shh' sounds as if it was rocking the shinobi to sleep like a baby with a lullaby. The shinobi manages to get out a "please" before the sand clamps over his mouth, choking him.
Gaara rips the shinobi apart; his arms go first. His legs go second. There is a muffled noise from the shinobi that Kankuro can only believe is screaming. The sounds behind the now rushing sands stop and start more times than Kankuro can remember. The body falls with a 'thud' like a sack of flour. The blood gushes out of the sack, and Kankuro almost has the will to vomit even though he has seen blood many times before.
The sand greedily maneuvers over the dead body, trying to soak up as much blood as possible, even slipping inside the body through the cuts made on the man's flesh. After the sand has its fill Gaara turns around and Kankuro has the urge to run, but can only stand there frozen as he gets hit full force with the smirk on Gaara's lips and in his eyes.
When Kankuro first sees Gaara give a teeth-wide grin, that he would later re-name Gaara's 'slasher smile', he almost faints out of pure shock and terror (not that he would ever admit this, but his wide eyes express as much). Gaara is fighting the green leotard wearing Leaf Village shinobi with the bowl-cut and leg warmers. He isn't worried, as he figures Gaara can easily take down a shinobi who solely focuses on taijutsu. What he isn't expecting is for the shinobi to break through Gaara's sand shield. What he isn't expecting is what is lying behind it.
He doesn't know what is worse: the bulging eyes that only hold the intent to kill or the rows of glistening white teeth in a mouth opening wide enough to cover three-fourths of a face, thereby making deep folds in the white skin around the mouth as if highlighting it. This smile is worse than the smirk. At first, Kankuro can't pin-point why. He thinks the teeth might have something to do with it, and they certainly make the face more frightening, but teeth are just teeth. A human can't use them to create much damage. His mind is running fast, but the fact that Gaara's teeth are not bared at him makes it possible to calm down. He wipes his clammy hands down his shirt, and begs his body not to portray his fear.
He tries to objectively study Gaara like he does with most of his opponents. To look at his facial expression is difficult, and he needs to figure out why. It was the glint in Gaara's eyes when he killed that sand shinobi that shook him to the core. This time…the eyes…they are different. They are worse.
Gaara at least had happiness in his eyes as he killed that shinobi so long ago. Now there is nothing, a smile with happiness even when killing is better than a smile that held no happiness at all. At least in Kankuro's mind at this moment as he watches Gaara crush the Leaf shinobi to disability.
When Kankuro first sees Gaara smile a 'normal' smile he is more shocked by it than the smirk and the slasher smile combined. It might be because he never questioned the smiles Gaara gave in the past. He knows his brother was unstable and fond of the appearance of blood. The smile he sees now though…he never expected it to make an appearance on his brother's face.
"Gaara let it go. I don't want to say this, but…you know how they see you. You're a weapon of terror."
They're standing out on one of the cliff edges in Sunagakure. The wind is blowing sand in their faces and the sun is beating down on their heads. He is standing behind Gaara as his brother looks outward at the sand dunes, and Kankuro wishes he knows what expression is on Gaara's face. Gaara tilts his head slightly giving his ear a better vantage point at which to listen to what Kankuro has to say, and Kankuro takes it as his opportunity to continue.
Kankuro closes his eyes. "Seriously, leaving us and joining the regular troupes is not gonna be an easy thing. They're full of Jonin who think pretty poorly of you." Kankuro stares at Gaara's blood-red hair as he continues, "And the villagers? They're as terrified of you as they've always been."
Kankuro waits for a beat, and Gaara responds. "I know that." Kankuro's eyes go wide. He has always thought his brother never paid any attention to how others feel. He isn't even sure Gaara knows how to read emotions or actions. Maybe…
And Gaara opens up. He tells him of his wish to be like that Naruto kid, of how he understands that life can bring pain, and suffering, and… joy, of how he wishes to be Kazekage. How he wishes to be seen as more than a weapon.
And Kankuro… he can start to begin understanding the way Gaara acts and why. A thing he can always do with his opponents if he tries hard enough, but never with Gaara even though he has been with him most of his life. Maybe what he needs to do is to stop looking at Gaara like the enemy, and the actions Gaara has made, and is making, and will make will start to blend together until Kankuro has a new image of the person standing in front of him that he can stick with.
Gaara turns around and smiles. Kankuro can only see half of his face, but it's enough just to be able to see. It's the first time Kankuro isn't scared of his smile.