The story of Bhai Dooj, a symbol of brother and sister's unwavering love and affection, is as follows
Chhaya is the wife of Lord Suryadev, who had two children, Yamraj and Yamuna. Yamuna loved her brother Yamraj very much. She always used to request them to come to their house and have food. But Yamraj used to postpone Yamuna because of his busy work.
Once Yamuna was invited by Karthik Shukla Dwitiya to eat his brother Yamraj, then Yamraj could not refuse and went to the sister's house. On the way, Yamraj freed the living beings in hell. On seeing her brother, Yamuna was very happy and welcomed the brother. Pleased after receiving Yamuna's sweet food, Yamraj asked the sister to ask for something. Yamuna asked him that - You will come here every year to dine with me and on this day, the brother who will meet his sister and the sister will provide food to his brother, do not fear him.
Yamraj obeying Yamuna said Aastastu and went to Yamlok. Since then, it has been recognized that the brothers who accept the hospitality of their sister to Karthik Shukla II do not fear Yamraj.