Sasuke has known for years that he is done being an avenger. He has known since the first time he felt a flutter of life under his fingers, cradled in his wife's womb.
He is a protector now. This is his role and his function and his reason to go on living. He is a protector, and he will do anything, let anything be done to him, in order to fulfill his mission. Just as he was willing to do anything and have anything done to him in the name of vengeance.
But his dead only smile at him in his memories.
His child -- his child only needs to catch sight of him.
He doesn't understand why the smiles; Sakura is the mother, the one who cares, and Naruto the funny-father, the one who jokes and tells stories and helps forget about skinned knees.
Sasuke is the stern-father, the one who poses the boundaries. The one who watches out and not in.
So the smiles -- the little smiles, the shy smiles, the hesitant smiles -- the sudden wide grins when his child forgets that Sasuke isn't the caring one or the funny one... he doesn't understand why. But he will protect them.
So when Naruto tells him to stop sleeping seated in a corner of the nursery, he tells him to fuck off. And when Sakura tries to puzzle out why all those older bullies take the long way around rather than walking by their street nowadays, he shrugs and changes the subject. And when Tsunade wonders how such an accident could happen -- these council members were experienced and crafty enough to know better, right? And if it was foul play, who would have anything against them? -- he arches an eyebrow and blandly asks she's asking him to investigate.
He already knows what he would find. Nothing. Because he left nothing. And he already knows why. Blackmail. Blackmail using his child.
Not on his life.
Sasuke is not tender, nor does he possess the kind of sense of humor that should ever be used around a child. He's cold, cynical. But it's alright. His child -- their child -- has Sakura and Naruto for that. He serves another purpose.
He isn't the funny one. He isn't the loving one.
So why.
Why.
The child is just enough like Naruto, that Sasuke knows the answer would be, "just because". The child is just enough like Sakura to add, "gifts are to be enjoyed and not questioned," if Sasuke ever, ever thought about asking.
Or maybe he would just receive a puzzled blink, and a shrug, and a smile. And then his child would fall asleep on him again.
Maybe this is answer enough.