To gain victory, the battle must be fought quickly. When Odin raises his sword it means he will soon use Zantetsuken (though it is not likely to happen in the 3D remake version). If Odin's sword is raised and any Thunder attack hits him, he will be halted on using Zantetsuken.
In the 3D remake version, Edge can steal the Darknessaugment and the player can guard against Zantetsuken in case Odin uses it.
If Kain has jumped and is out of the battle when Odin uses Zantetsuken, he will not be affected. Rydia is needed most in this battle. If the player is getting overwhelmed, it may be easiest to set the Battle Speed to slow.