Demon Banasura had attained a boon that a virgin girl will only kill him. The demon believed that he could easily overpower a young virgin. After getting the boon, Banasura defeated the Devas and started numerous Adharmic activities.
Vishnu advised the Devas to pray to Goddess Shakti to find a solution. Goddess Shakti promised the Devas that She will restore Dharma by annihilating Banasura.
Goddess Shakti then appeared as a beautiful young girl on earth. Banasura who came to know about the beautiful girl decided to take her away forcibly. Goddess Kannyakumari easily overpowered the army that was sent to take her away.
Banasura sent numerous armies and demons overpower the Goddess. But all of them failed.
Finally, Banasura himself went into war with the Goddess. After a fierce battle, Goddess Kanyakumari used the Chakrayudham (disc) and killed the demon.
A legend associated with above story states that Shiva who came to know about the beauty of the Goddess Kanyakumari wanted to marry her in this form. But if the marriage takes place, She will no longer be a virgin and will not be able to kill Banasura.
To stop the marriage, Devas approached Sage Narada, who played a trick on Shiva. The marriage party was to reach Kanyakumari in South India at a particular time. The marriage party reached the vicinity on time but Sage Narada took the form of a cock and crowed. Shiva thought he had missed the auspicious time and returned.
Goddess Kanyakumari waited for Shiva for a long time. When Shiva did not turn up, She became furious and threw out all ornaments, vessels and food that was prepared for the marriage. Whatever the goddess threw out became seashells and sand. The abundance of colored seashells and sand at Kannyakumari Beach in Tamil Nadu in India is attributed to this legend.
Goddess Kanyakumari is worshipped as Kumari Amman and Devi Kannyakumari at the famous temple in Kannyakumari in Tamil Nadu.