The defense buff you get from Divine Avalanche is positional (melee) rather than typed (smashing, lethal, etc.) The synergy is strongest with the defense sets that also offer position rather than type defense. But since you can't run Shields with Katana, this basically leaves Super Reflexes and Ninjitsu as the obvious choices.
You might also consider Regen, especially if you want a whole-game rather than an endgame character. Characters like that are valuable additions to anyone's roster, even if they aren't good for master runs. Build them for running Synapse and Citadel as fast as you can, with double inf/no XP when exemped. Regen gets hardly any defense, so adding a layer of melee defense that's indifferent to type adds value.