-( Story related, cannot be missed )-
Crimson Helm has occupied the depths of the Gale Shrine, tainting it with malice and holding the Serpent Crystal for itself. Without that crystal, the barrier around Orochi's Moon Cave cannot be lifted, so you HAVE to defeat him. He is a simple two-armed bull creature that is heavily fortified. For the most part, you will need to attack his armor to make him shed it. Once that has been shed, use Galestorm to extinguish the flames and then attack. Repeat this strategy while avoiding his attacks (which are rather predictable and dull).