By Charles Gilman
My first Shogi variant, Mitregi, adds a Europeanising balance between the orthogonal and the diagonal. TUNNELSHOGI extends this principle to all 3 types of radial on a 4x4x8 board much as Tunnelchess does FIDE pieces. It has a separate page because it has relatively few pieces in common with Tunnelchess. Having only 2 empty ranks between the two 3-rank camps keeps up piece density, as does less than doubling the files by retaining the familiar division of files into Frame (a, d, m, p), Wall (b, c, e, h, i, l, n, o), and Tunnel (f, g, j, k).
The 3d character extends to the pieces' flip properties. Shogi itself uses three kinds of 180º rotation: a YAW around the axis at right angles to the board, for unpromoted pieces reintroduced after capture, a ROLL around the axis of the files, for promotion; and a PITCH around the axis of the ranks, for promoted pieces reintroduced in demoted form. 4-player Shogi variants such as Yonin Shogi add a 90º yaw, for capture by non-opposite armies, but Tunnelshogi adds a 90º roll, for alternative promotions. Pieces promoted to one of two alternatives can be promoted to the combination of them on returning to their own camp.
The same symbol in opposite orientations always represents one of the following types of pairing:
(1) a symmetric piece and its forward-only version (Rook/Wing, Bishop/Mitre, Unicorn/Horn);
(2) two generals with the same symmetric compoment (Gold/Brass, Silver/Steel, Azure/Jade).
Names of forward-only pieces and enhanced linepieces are from my piece article Constitutional Characters, as the original Japanese names are not easily extrapolated. I suggest marking pieces with big Rook, Bishop, and Unicorn figurine symbols for the moves of those pieces and small versions for lesser moves in the same kinds of direction. If you colour unpromoted and promoted markings differently, intermediate promotees should have a third colour. Loyalty is determined by orientation, with a pointed far end (towards the enemy camp). Three pieces NOT occurring in Tunnelshogi but useful for understanding those that are, as components of them, are the Wazir, moving one step in any of the Rook's 6 directions; the Ferz, moving one step in any of the Bishop's 12 directions; and the Viceroy, moving one step in any of the Unicorn's 8 directions.
The PRINCELING (could be unmarked) moves one square straight forward or in any of the four forward standard (2d) diagonals. All five moves can be capturing or non-capturing. This allows some Pawn structure lacking in standard Shogi. It can become a Goldgeneral or Silvergeneral (see below) on reaching the enemy camp, and must on the furthest rank. The promoted piece can in turn become a PRINCE (marked with small King symbol), combining the moves of both generals, on returning to its own camp.
Sharing the 2nd-rank Wall squares with the familiar ROOK and BISHOP is the Raumschach UNICORN, which moves along the nonstandard diagonal (colloquially called triagonal). Note that the number of pieces here has been quadrupled, partly to double the total number of pieces but mainly because they are the strongest pieces. Intermediate promotion adds a one-cell move in another kind of radial direction. A Rook can become a CHATELAINE (Rook+Ferz) or VICEREINE (Rook+Viceroy), a Bishop can become a PRIMATE (Bishop+Wazir) or MODERATOR (Bishop+Viceroy), and a Unicorn can become a BESIEGER (Unicorn+Wazir) or HERETIC (Unicorn+Ferz). Suggested markings: the small symbol for the added direction type INSIDE the big symbol (e.g. small Bishop in big Rook for Chatelaine). On returning in promoted form to their own camp they can acquire a one-cell move on ALL remaining radials. The promoted Rook becomes a PEERESS, the promoted Bishop a POPE, and the promoted Unicorn a USURPER. Suggested markings: a small King symbol inside the big symbol.
On the back rank are six kinds of general. Tunnelshogi inherits the GOLDGENERAL and SILVERGENERAL but on a more equal basis, for while the former still has the more balanced mix of moves - 6 Wazir and 4 forward Ferz moves - the latter gains the greater total - 12 Ferz and 1 forward Wazir move. Their antiquity is marked by their sharing the ends of the Tunnel with two Tunnelchess EMPERORS.
At the ends of the Frame files are four newcomers whose names are more fully explained in my piece article Generalised Generals: BRASSGENERAL (Wazir+FO Viceroy), STEELGENERAL (Ferz+FO Viceroy), AZUREGENERAL (Viceroy+FO Wazir), and JADEGENERAL (Viceroy+FO Ferz). Suggested markings: for the Emperor a large King symbol, for generals the relevant small symbols, the symmetric component (as the stronger) ahead of the FO one. Generals have only an enemy-camp promotion: Gold and Brass to SUNGENERAL, Silver and Steel to MOONGENERAL, and Azure and Jade to COASTGENERAL. Each promotee combines the moves of the pair promotable to it and so can move one cell in, among others, all nine forward radial directions. Suggested markings: the symbol for the symmetric direction ahead of a small King symbol.
Behind the linepieces on the Wall files are forward-only versions of them, or rather of each other. WING, MITRE, and HORN are my hopefully self-evident names for the respective forward-only versions of the Rook, Bishop, and Unicorn. Suggested markings: small symbols with arrows ahead pointing toward the enemy camp. Promotions are to generals: intermediate ones respectively Gold or Brass, Silver or Steel, and Azure or Jade; and return ones respectively Sun, Moon, and Coast.
Captured pieces can be reintroduced as in Shogi, in unpromoted form and, in the case of FO pieces, not on the far rank. As in most of my 3d and/or 4-player variants, there is no castling. Checkmating either Emperor wins the game. It may also be worth allowing a win by baring the Emperors - i.e., a player with Emperors but no capturable pieces, on board OR in hand, loses.