Kain... my best character.
Here's two ridicuolously (In my opinion) op combos.
Onion Knight assist btw
1. Hit Crashing Dive, making sure you stomp them onto the ground. Onion Knight assist. And right as the last Blizzard hits and knock them up, use rising drive.
2. Kinda of the same as the first. Hit Celestial Shooter making sure you hit them against the ceiling of the map and then hit Sky Rave.
Its so good its almost unfair.
And if i remember correctly, theres a combo that works with Gilgamesh and Gabranth.
Hit Tsubamegaeshi and when the enemy hits the ground, Gabranth assist. RIght when you recover go for Tsubamegaeshi again and this time when the enemy hits the ground, Gabranth should have just finished his combo and will nail the last hit ( knockback ) on the enemy. If that last hits slams them into a wall you can go HP attack on them.
And Lighting.
If i remember right, if you are close enough when you hit Aeroa, you can hit Lighting Strike right afterwards.
There was something else with Blizzara and Thunderfall that i cant remember.