Beschreibung
Capture your opponent's last queen to win.

4 variants (4 2-D perspectives of a spherical, 3-D game):

white whole | black quartered (shown below)
black whole | white quartered
white halved N & S | black halved E & W
black halved N & S | white halved E & W
A draw is impossible.
Each player begins the game with 8 queens.
Once the last queen of either player has been captured, the game will end immediately.

The pendulum-move rule applies which dictates double-moves alternating between the two players throughout the game except for the very first move which is only a single-move by white.

All available 4-, 5-, 6-, 7- directional moving pieces can be half-promoted into pieces with 1 additional direction of movement at the cost of 3 moves.

All available 4- & 6- directional moving pieces can be single-promoted into pieces with 2 additional directions of movement at the cost of 4 moves.

All rooks (4-directional moving pieces) can be double-promoted into queens with 4 additional directions of movement at the cost of 6 moves.

All pieces capable of movement can capture by replacement any enemy or neutral pieces.

Portals connect opposite edges along all 8 geometrically-contiguous directions of linear movement possible within the square-spaced, flat 2-D gameboard.
Consequently, 8 directions of movement are available from every square-space within the flat 2-D gameboard.
Essentially, this is a spherical surface, 3-D chess variant that can be represented accurately and played well using as few or as many of the 4 available, congruent opening setups as desirable within the flat 2-D gameboard due to its exclusive usage of 2-D pieces.
This means that an entire game played via any 1 given opening setup can be completed transposed, move-by-move, into entire games played via all of the other congruent opening setups.
Notably, the naive appearance of geometrical asymmetry in 2-D between the two armies with any given opening setup is totally illusionary.
When the fact that the 2-D gameboard has no real edges in any way (i.e., continuous space), despite its flat 2-D representation to the contrary, is taken into account, the positions and available moves for all of the 2-D pieces of the white army, relative to everything (friendly pieces, neutral pieces, enemy pieces and empty spaces), are mirror-image symmetrical to those of the black army.
In reality, a 4-fold, perfect, holistic 3-D geometrical symmetry applicable to the surface of a sphere exists for this game despite the limitations due to its flat 2-D representations.

This is the disadvantage to using flat 2-D representations of a spherical-surface, 3-D chess variant.

The 2 most symmetrical, representative, opening setups (white whole - black quartered & black whole - white quartered) out of 4 available maintain perfect quadrilateral symmetry in 2-D by north-south, east-west, northwest-southeast and northeast-southwest axes.
The playing surface consisting of a finite, 2-D plane with a square-spaced, flat 2-D gameboard of 20 x 20 spaces (400 spaces total) and a square shape overall (apparently) is perfectly mapped onto the surface of a finite 3-D sphere.

[Note: The true shape overall of the square-spaced, flat 2-D gameboard is actually circular. This is not obvious. Instead, it appears to be square due to the commonplace elongation of the diagonal dimension and/or shortening of the orthogonal dimension which is the universal convention for representing them.
This implicates why a perfect mapping onto the surface of a 3-D sphere, from a circle rather than a square, is ideally suitable and achievable.]

Fortunately, the players are not required to deal with any complex, confusing 3-D curvature characteristic to a spherical playing surface.

This is the advantage to using flat 2-D representations of a spherical-surface, 3-D chess variant.