This is a web-published DIY 4 player version of shogi, a game also called Japanese chess.Each player sets up pieces as usual on the 4 back-rows of a shogi-ban (shogi board). In the center are 3 sets of a row of 9 spaces, one each to be shared between each possible pair of players. That shared row acts as a fifth row of a board shared by a given pair of players; only those two given players may nter or cross through the space. As usual orientation of a piece marks ownership. All standard rules of shogi apply.
For a 3 player version, one player's partial board is simply eliminated.
Gameplay is clockwise. To use Western terminology, a player whose "king" is checkmated at the start of their turn-- whether by a single player-s pieces or by a combination of players' pieces-- is eliminated. The "king" is removed from the board" and thereafter that player's turn is skipped. The last remaining player wins.