Triple Crown

What these variants have never developed is the three single-step moves straight across the centre of the board. They essentially treat the centre as a singularity, with orthogonal moves to a cell 60° round the centre and diagonal ones to a cell 120° round it, but none to the opposite one. This variant tackles the straight-across step by treating it as a very limited root-3 diagonal - more akin to the two-level cubic one than to the hex one because of the coexistence with the standard (root-2) diagonal and connecting cells of opposite Bishop bindings. This restricts pieces using it to the Viceroy and its compounds with square-board pieces. This suggested to me the threesomes (on cubic boards, and hence also on this one) of Crowned Rooks and Crowned Bishops which, as in most places triagonally-crowned pieces would behave the plain FIDE linepieces, pushed me to an array modelled on Duke of Rutland's Chess and my offshoot Modern Manners. The existence of three types of each gave me the name. I went for an extrapolation of a 10x10 board to 15x15, noting that with this kind of geometry each rank intersects only two-thirds of the files and vice versa.

Other variants of mine with a 6-cell centre are the "standard" 96-cell Fiancé Chess and the smaller Triana.

Setup

Pieces

Crowned Rooks:
The CHATELAINE, represented above by its initial C, is a Rook that can also make the one-step diagonal move of the Ferz. It cannot move straight across the centre of the board.
The VICEREINE, represented above by its initial V, is a Rook that can also, should it find itself on a centre cell, move to the opposite centre cell. It cannot move diagonally.
The BARONESS, not occurring in an array, is a Rook that can do both.

Crowned Bishops:
The PRIMATE, represented above by Pm (as distinct from Pn for the Pawn), is a Bishop that can also make the one-step orthogonal move of the Wazir. It cannot move straight across the centre of the board.
The MODERATOR, represented above by its initial M, is a Bishop that can also, should it find itself on a centre cell, move to the opposite centre cell. It cannot move orthogonally.
The POPE, not occurring in an array, is a Bishop that can do both.

Enhanced Royalty:
The EMPEROR, represented above by its initial E, is a King that can also, should it find itself on a centre cell, move to the opposite centre cell.
The DIARCH, not occurring in the array, is a Queen that can also, should it find itself on a centre cell, move to the opposite centre cell.

Rules

Castling involves any of the following four pairs of moves, in abbreviated descriptive notation:
E-EM1 and EV-EPm1;
E-EM1 and EH-EPm1;
E-QM1 and QV-QPm1;
E-QPm1 and QC-Q1.
As usual all intermediate cells must be empty at the start of the move and no part of the Emperor's path may be in Check from either enemy.

A player must promote a Pawn reaching either far rank. If they no longer have the full quota of symmetric array pieces, and have no non-array pieces, they must promote it to one of the missing pieces. If they still have the full quota, or have regained it through previous promotion, they must promote it to a Baroness or a Pope, subject to not having more than one of either, or if they have both a Diarch. A player with a Baroness or Pope but not both must promote to the other, and one with both must promote to a Diarch.

A player whose Emperor is En Prise to the player about to move is Checkmated and their pieces removed from the board - but never forget the possibility of escaping Check straight across the centre! The checkmating player then makes their move and play proceeds with the remaining players. The first player checkmated loses and the last to survive wins. A player can also win instantly, regardless of the number of other remaining players, by getting a Pawn to a far rank when they already have all three non-array pieces.