He transforms to this state either at will OR if his personal item, the Cosmic Star overcharges and releases the excess Light energy.
During this state, Takua has hyper-charged strength and speed. His Light powers are amplified to great levels. Takua also gains super sharp armblades. He's even granted limited invincibility, thus a Makuta like Teridax can't affect him that much.
His Cosmic Star has an ultra-high energy capacity, so he can remain in this form for a long time. When the Star runs low, he automatically changes back.
Rashzakea and I came up with the original two designs, his being more complete looking and mine being more easily edited by using different technic parts. That said, well done on this MOC. I especially like how the blades are an actual part of his arm instead of just stuck there.