As a child and as an adult, Amir is haunted by the blood on his hands. It begins when he is born and his mother dies giving birth. He feels so alienated from his father that

... I wished I could open my veins and drain his cursed blood from my body.  (Chapter Four)

Amir enjoys the bloody hands he receives from the pleasurable hours he spends flying kites with Hassan, but his victory at the kite flying tournament is marred forever by the blood spilled by Hassan after he is raped by Assef. Hassan successfully returns with the prized blue kite, but Amir has refused to help his Hazara friend when he most needs it, and

... I pretended I hadn't seen the dark stain in the seat of his pants. Or those tiny drops that fell from between his legs and stained the snow black.  (Chapter Seven)

Afterward, Amir takes out his guilt on Hassan with pomegranates, leaving him

... smeared in red like he'd been shot by a firing squad.  (Chapter Eight)

There are many more instances of blood that continue to haunt Amir, from the blood that Baba coughs up before he is diagnosed with cancer to the nightmares he endures after he learns of Hassan's death.

His knees roll on the hard ground and bleed through his pants as he rocks in prayer...
     The rifle roars with a deafening crack.
     ... I see the face behind the plume of smoke swirling from the muzzle. I am the man in the herringbone vest.  (Chapter Nineteen)

Amir's own blood serves as a form of atonement when he is beaten by Assef.

My body was broken--... but I felt healed. Healed at last.  (Chapter Twenty-Two)

And Amir resorts to prayer after Sohrab attempts suicide and he sees the boy's "bloody feet" poking out from the hospital gurney. With "blood thudding in my ears," Amir bows to the west and kneels on his prayer rug, pleading to his God that the blood-letting will finally end.