If Zelos expected Kratos to be deterred by the mere threat of battling an Aegis, then Zelos has forgotten who exactly Kratos considers his brother. So Zelos' bluff and bluster don't mean much to him, and he pays them hardly any mind. He's confident enough that he could win this fight, and if not, then certainly he will know when to yield before his life is threatened.

The point is not to win, anyway. It is to make sure Zelos is certain, certain that this is a decision he wants to make, is willing to fight for, and not a path he intends to take simply because it is easy.

Kratos gathers his energy and his ether.

Breathes.

Moves.

Light blades have the ability to lean into their element and cross short distances in the blink of the eye, and Kratos uses that to place himself in front of Zelos, now. Once before the Aegis, he holds out his hand and sends a blast of ether at Zelos.