King — one step, any direction.
Sulfur — leaps exactly two squares in any of the eight directions, clearing any piece in between.
Sun — moves orthogonally, any distance.
Mercury — moves diagonally, any distance.
Psi — orthogonic movement.
Salt — one step in its own forward direction, capturing one step diagonally forward. All pieces may also move between the two boards — as a nexus between the noumenal and causal. Air & Fire pawns advance up/down the board; Water & Earth pawns advance across.
A piece may either
move or capture vertically to its own square in the other board.
A
throne square (i.e. the four corners) starts held by a king and a partner piece together as a cell. If the throne cell is captured while both pieces occupy it,
both pieces fall at once.
A king
in check must move if it has any legal step at all, even into another check — only if it is cornered by its own side may another piece be played instead.
When a king is captured, its entire army is
frozen: the pieces stay on the board as obstacles, but can never move, threaten, or be captured again.
A pawn promotes to the piece it served (sulfur, sun, mercury, or psi) on reaching the far edge — but only once that piece has already been lost.
Allies never threaten or capture one another. The game is won when
both kings of an alliance have fallen.
Air — sona, Water — pilin, Fire — wile, Earth — pali
The teams are coloured as such in re-presenting their core physis expressed in the system of Solresol. That is, Air as do, Water as fa, Fire as so and Earth as la. These in their dictionary given as the following meanings:
do: man, his body and spirit, intellectual faculties, qualities and nourishment;
re: clothing, the house, housekeeping and the family
mi: man's actions and his flaws
fa: the countryside, travel, war, the sea
sol: fine arts and sciences
la: industry and commerce