It ends with Amir and Sohrab kite fighting. Sohrab has sort of taken on his father's role but as Amir is now the one running for the kite and not Hassan, the roles have reversed. Amir will do anything for Sohrab, just as Hassan would have done anything for Amir. Amir is the one who now says: 'for you a thousand times over' to Sohrab just like Hassan had said to Amir. That is how the book is full circle