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@ Fergus:

I discovered that when I go to the list of all comment subjects and click on this particular subject, the next thing I see is (unexpectedly) all the old comments (on various subjects) starting in 2002.

Tai Shogi features a royal Kraken (called Emperor), and in Maka Dai Dai Shogi the King can promote to such an Emperor. To make this work, there is a sort of anti-trading rule for Krakens, similar to the Lion-trading ban in Chu Shogi: an Emperor is not allowed to capture a protected Emperor. Or actually, it is not allowed to capture any protected royal (you can have multiple royals in these games.) The historic rules are not entirely clear, and some interpretations are even that it can never capture any protected piece. (Mostly moot, as doing so would lose you your Emperor, which you certainly would not want.)

This issue is related to the definition of check, whether it is in terms of pseudo-legal moves (as in FIDE Chess), or in terms of legal moves for capturing the King. Or, in other words, whether the checking rules are applied front-to-back or back-to-front. In FIDE rules a piece that is pinned on its own King can still deliver check; that by actually capturing the King it would expose his own King to capture is of no import. In a recursive formulation of the rules a pinned piece would not deliver check, because the ban to expose its own King weighs more heavily than the fact that it captures that of the opponent. Its captures would not be legal moves, so the opponent King can safely go to the squares that the piece would target if it had not been pinned.

Under the recursive rules you could also step next to the enemy King as long as you are protected. In any contiguous sequence of captures of royals, it would be the last capture that decides the game rather than the first. So the game proceeds as long as royals can be captured, even when the player making such a capture has already lost all his own royals. (This is reminiscent of the Shatranj baring rule, where King baring doesn't grant an instant win, but the opponent gets one more turn to also bare the other King.)

A royal Kraken is perfectly feasible with these recursive checking rules; as long as you keep it protected it is save from capture by its counterpart. (Not that it would make a very nice game, IMO; a royal Kraken is very hard to checkmate, so you can only win by practically exterminating its entire army, so that there is no way to keep it protected against capture by your own Emperor. So the game loses the character of Chess, with a royal piece that has to be protected at all cost, and becomes more Checkers-like.)

For a non-royal Kraken you can solve it by some ad-hoc rules. Like that a Kraken capturing royalty becomes 'tainted', and that the game ends on the following conditions, applied in that order:

1. When you capture a tainted Kraken, you win
2. When you had no royal before your move, you lose

It would also be possible to simply declare the royal immune to Kraken capture. This would be more a property of the King than of the Kraken.

That's now fixed. Thanks for pointing it out.

Thanks for your detailed and erudite reply, H.G.

Kevin

It occurs to me it may be possible to have classes of variants that are interesting which have one royal kraken per side, with an anti-trading rule (i.e. both krakens must stay protected, or else they would be captured by the opposing kraken). That's provided each side also has a royal king that's ruled immune from kraken capture or check, and/or each side has an anti-king (again immune from kraken capture, but also not in any way in check by it).

One strategy of such variants might then not be necessarily to checkmate the other side's kraken by eliminating its army, but rather to now and then check the other side's kraken with other pieces, forcing said kraken to move to a different protected cell, or the owner to play another kind of disadvantageous move, to block the line of attack against it. The idea would be that this produces a weakening of the defences of the more realistic target, which might be the royal king (and/or anti-king, alternatively).