On the day the kyuubi caused havoc in the leaf village, Minato sacrificed himself to save the village and his newborn twins' lives by sealing half of the kyuubi for Naruto and half for himself. Kushina, the 4th Hokagr's wife and the mother of the twins, can't accept the fact that her husband is dead, so she left the leaf along with her daughter Mito and chose to abandon Naruto because of the Kyuubi inside him. Smart Naruto Abandoned Naruto