Once the battle begins, collect any hearts around the island you may need. You can also use this place for some health restoration when needed. Afterwards, dive off the edge and call your Loftwing.
Once you do, the battle begins. It is actually quite simple – there are four eyes trailing behind Levias. You are to Spiral Charge into all four.
The bad thing is that this battle is pivotal primarily based on your control of a Loftwing (which is hard enough in this game when you demand accuracy).
Then there is the fact that Levias is about as fast as you, so if the tail or eyes’ optic nerves hit you, you lose a heart.
I tend to try to approach Levias from the side. He is generally circling during this battle, so I kind of make a chord in the circle to beeline for where his tail end will be. Then I try to Spiral Charge an eye and repeat.
The battle ends once you eventually hit all four eyes.