I believe that any Akuma is a great combination with Rengoku. They all use illusions and, with their True Samurai Spirits, stack a ton of damage on top of that. Truthfully, you can use any bloodline with Rengoku. It is up to you, in any situation and whatever bloodlines you have, to create a combo of your own. This is one of the best parts of Shindo Life; every combination has the potential to be a devilish duo of destruction.