Single Comment

The knight here has of course just two moves in its lifetime.  Dropping a knight becomes a tricky subject (although I suppose in my few Shogi games I rarely want to drop a knight).

I assume the proposed promotion zone is the last hyperrank?

I think I would suggest different diagonal movement in this game.  As many of the Shogi pieces see 'forward' differently than 'sideways', it is perhaps better to keep track of the two 'forwards' and the two 'sideways' directions in this 4D board.  In particular, I think the moves from center square Bb2ii should probably not include Bb3iii, nor any of the extended diagonal forward&back like Bb1iii.

I also think that there's a possibility that king restriction (beyond eliminating tri- and quad-ragonals) is unnecessary.  This board is so compact that the dense moves of the generals, the enemy king, and especially an enemy dragon king or dragon horse could force mate.  (In fact, if 3- and 4-diagonals were included, a dragon on the center square sees everywhere.)

(And Charles, Daniil's sentence is fine with the omission of those commas and replacing 'which' by 'that' (a grammatical technicality not recognized by most).  I think such cells will occur infrequently enough to not warrant a universal name; one needs a particularly asymmetric piece to have any such squares.)