On the first day of Deepawali, also celebrated as Yamadeepdaan and Kaag Tihar , lamps are kept burning through the night in reverence to Yama and his messenger — and prayers offered to him to keep away death and despair. The second day, which falls today and which is celebrated as Narkachaturdashi, originates from days of Lord Krishna. Yama is also worshiped on this day to get over the fear of demon Narakasura. The most popular story associated with this day is that of Satyabhama and Narakasura. Narakasur was a demon king who ruled Pragjothishyapur. He received a boon from Brahma that he would die only in the hands of a woman.
Addicted to power, he defeated Lord Indra and stole the earrings of Aditi (mother goddess). Aditi was a relative of Satyabhama. When she heard of the injustice being done to women in general by Narakasura and his behaviour with Aditi, she was enraged. Satyabhama went to ask Lord Krishna for permission to wage a war against Narakasura. Krishna not only agreed, but also offered to drive her chariot in the battlefield.
On the day of the war, both the armies fought bravely and the war continued for some time. Satyabhama fought Narakasura bravely, but she was no match for his trained war wisdom. After some days, when Narakasura got a chance, he took an aim at Krishna, hurting him lightly. Krishna fainted and made Satyabhama furious. She doubled her attack on the demon king and killed him finally.