If we stayed with classic Feudal Japan heirachry then the obvious choice would be Emperor. The likely choice of anything above the Emperor would be a Deity, though the Emperor was considered a Deity.
It could be like:
Daimyo 500 dks
Shogun 1000 dks
Then once Emperor was reached (around 8000 dks?) the first Emperor could be 1st Emperor, then all others would be listed in the order of who reached Emperor as there shouldn't be anything after that. I think that would work out as the only people that would go all the way to Emperor would be super-hardcore players and it's probable to think that there will be no more than 50 or so after another year. If you'd like more once 1000000 dks were reached (I'm serious) there could be something else like a form of Deity.
It'd also be nice for the possible missing-nin that are coming to have a bounty instead of a rank. Like in One Piece ( recently picked up on the series ) where the really infamous Pirates have millions of (whatever the currency is ) on their heads.