Kacha is the son of Brahaspati, the Guru and leader of Devas (heavenly people). Devayani is the daughter of Sukracharya, Guru of Asuras (Demons). Frequently Devas and Asuras went to war with each other. Sukracharya knew a mantra called mridsanjeevani which has the power to revive the dead back to life. Therefore, whenever there was war, the Asuras who were killed were brought back to life whereas Devas lost their men.

Devas decided to send Kacha as a disciple of Sukracharya and told Kacha to tactfully learn the mridsanjeevani mantra. Kacha went to Sukracharya and introduced himself as the son of Brahaspati and requested Sukracharya to accept him as a sishya (disciple) for 1000 years. Sukracharya gladly agreed. Devayani saw Kacha and fell in love with him. The Asuras came to know that Kacha is the son of their enemy and they waited for an opportunity to do away with him.

500 years has passed. One day Kacha herded Sukracharya's cattle to the forest to feed them. Asuras decided this is the opportunity for them as Kacha was alone. They also went to the forest, killed Kacha, cut the body into pieces and fed the tigers. When the cattle returned home without Kacha, Devayani was anxious. She told her father that someone must have killed Kacha and asked her father to revive Kacha's life as she is in love with him. So Sukracharya used his mantra and revived Kacha who returned from the forest hale and hearty.

After some years had passed, Kacha went to the forest again, this time to pluck some rare flowers. Asuras killed him again. They burnt his body and took the ashes. Then they mixed the ashes with a drink and offered it to their Guru who drank it. Again Devayani pleaded with her father to revive Kacha. Sukracharya responded, "He is in my stomach now. If I revive him, he will tear my body and come out. So, I will die. Tell me whom do you want to be with, he or me?" Devayani was in a dilemma. She said he has to offer some other solution because she needs both Kacha as well as her father.

Sukracharya pondered for a while and realised that there was only one way to solve this. He taught the mrdisanjeevani mantra to Kacha who was inside his stomach. Kacha learned it thoroughly. Then Sukracharya chanted the mantra and Kacha came out tearing away Sukracharya's body. Sukracharya died. However, Kacha chanted the mantra and revived Sukracharya.

When the 1000-year period was over, Kacha informed Sukracharya that he wished to return to heaven. Sukracharya agreed and allowed him to go. But Devayani stopped Kacha on the way and asked him to marry her. Kacha refused saying she is his Guru's daughter and therefore she is also like a Guru to him. Further, he said, as he was reborn from the stomach of Sukracharya, and hence felt Devayani is like a sister to him.

Hearing this, Devayani went into a rage and cursed him that when a need arises, Kacha will forget the mantra he learned from her father. Kacha was hurt and cursed her that no Brahmin will marry her and that whatever she wishes, will not happen. Thus ended the lives of both Kacha and Devayani.

The efforts by Devas were in vain and they were in the same plight. They prayed to Lord Shiva who advised them to go to Lord Vishnu. Consequently, Vishnu brought them immortality through Amrita.