Disclaimer: I don't own Naruto.
Sakumo's breathing is shallow at night, and it makes Kakashi nervous.
It is late at night, the only light being moonlight filtering through an opaque window. Kakashi sleeps on a tatami mat next to his father, but tonight he is awake, unable to sleep and unwilling to bother his father to get him a glass of water.
At five years old, Kakashi is perceptive enough to know that his father is different from other men. His father is strangely sad and quiet, a heaviness hovering in his aura and a bleakness in his eyes.
Sometimes on the nights when Kakashi can't sleep or won't sleep, he sits up in bed, and watches his father breathe.
Sakumo's face doesn't slacken when he sleeps; it retains all its marks of haggardness and its lines of worry and sadness into slumber, and there is a new, added feature that comes to linger in the darkness and is banished with the rising of the sun.
His breathing is shallow, far too shallow for Kakashi's liking. It is not deep and stately as when his father is in repose or thinking hard, not quick and slightly belligerent as when he and Jiraiya have one of their famous discussions, but fluttering and pulsing. He sleeps as though his heart is running a marathon and can not draw in breath to save his life.
He sleeps as though he is on the point of death, his careworn face going slack yet terribly tense with some unknown fear, some unknown monster prowling in the fog of his dreams.
On nights like this, Kakashi too has trouble breathing. And on nights like this, Kakashi sits up through the night, watching his father's breathing, afraid that if he does not, Sakumo might die during the night, and wishing he knew why.