It was around this time that King Daksha [the father of Sati, the first wife of Shiva] got one of his daughters, Murti, married to Dharma (Yama, God of Justice) - one of the 'Mind' sons of Lord Brahma, the God of Creation [It is said that Lord Brahma created his mind sons or Manas putras from his thoughts]
Murti had also heard of the atrocities of Sahasrakavacha and wanted to put an end to his menace. So she prayed to Lord Vishnu to come and help the people.
Lord Vishnu pleased with her, appeared before her, 'Murti! I am pleased with your devotion! I will come and slay Sahasrakavacha! Because you have prayed to me, you would be the reason for slaying Sahasrakavacha!'
Murti was happy. Subsequently she gave birth to not one child, but twin sons. She named them as Narayana and Nara. Nara Narayana was the fourth avatar of Sri Vishnu.
Narayana and Nara grew up as sages in the ashrama surrounded by the forests. They live at Badrika performing severe austerities and meditation for the welfare of the world. These two inseparable sages took avatars on earth for the welfare of mankind. They enjoyed praying to Lord Shiva. Their mother also encouraged them to learn fighting. The two brothers learnt the art of warfare.
In the concept of Nara-Narayana, the human soul Nara is the eternal companion of the Divine Narayana. The two brothers were inseparable. What one thought the other was always able to finish. Both of them trusted each other implicitly and never questioned the other.