There was a demon who used to on feed people and gods weren’t able to defeat him. So all the gods decided to become his friend by as asking hand for marriage. He accepted the proposal, young beautiful girl go married to him. So as all the villagers were his in-laws now, so he went to the land of demons with his newly wed wife, but as the girl was a human being so she died shortly after living with the demons.
Now the whole valley was cursed and people started dying as they sacrificed the life of an innocent girl, so Manu took step and told that he would celebrate a festival to appreciate the sacrifice made by the poor girl. Then after some time the curse was removed from the whole valley and people started to live happily.
Till date this festival is celebrated and the soul of the girl and her husband demon are invited over the valley to celebrate and appreciate her sacrifice.