The story
Skanda — Murugan in Tamil, Kārttikeya and Subrahmaṇya elsewhere — is the son Śiva produced to end the demon Sūrapadma, who could not be killed by anyone older. He was raised by the six Kṛttikā stars, which is why he has six faces, and he took the spear (vel) from his mother.
The battle ran six days. On the last of them Sūrapadma took the form of a mango tree; Skanda split it with the spear, and the two halves became his peacock mount and his rooster banner. The demon was not destroyed but taken into his service, which is the part of the story the tellers dwell on.
In Maharashtra the same tithi is Campā Ṣaṣṭhī, kept for Khaṇḍobā at Jejuri, a form of Śiva that scholars and devotees read together with Skanda.
