Yonin Shogi

Yonin Shogi is a four-handed Shogi variant which can be played on a regular Shogi board if one has two sets of pieces.  George Hodges credits the invention of this game to Ota Mitsuyasu, mayor of Hirata City.  An extended introduction will replace this one when some more information about the history of this variant is acquired.

Setup

The four players sit on the four sides of the board.  On their back three rows, in the five central columns, each player starts with the following setup, with pieces pointing away from them as in Shogi:

--P--
-PRP-
SGKGS

P: Pawn
R: Rook
S: Silver
G: Gold
K: King

Pieces

All pieces move and promote as their Shogi counterparts.  Note that since there are four players, each promotion zone overlaps with two others.

Rules

All rules, unless stated otherwise, are identical to those of Shogi, including pawn drop restrictions.  I am unsure of the rules to determine who goes first, but play is clockwise.

There is also a way to play in partnerships, but I am not clear on all of the rules regarding what is or is not legal.

When a player is put in check, the turn shifts immediately to them.  If at any time, two or more players are simultaneously in check, whichever one would go first according to the regular turn order gets to go next.  If one player is checkmated, then whoever made the last move (not necessarily the player who originally gave check) counts as having checkmated them.

When one player is checkmated, the checkmating player flips over their king, takes all their in-hand pieces, and takes control of their on-board pieces from that point on.  (Flipped kings act as blockades, and no piece can capture or pass over them.)  When you take control of another player's pieces, they still retain their orientations and promote in their original promotion zone.  You cannot capture your own pieces, even if they are facing a different direction, and you may only ever drop pieces so they face in your own original direction.

The first player to checkmate two others, or to checkmate a player who has already checkmated another, wins.

Notes

Any additional information pertaining to Yonin's history or any corrections or additional info regarding the rules would be greatly appreciated.  All the information I have was gathered from tinkering with the Yonin Shogi game for Super Famicom while not being able to read any of the Japanese text therein.  (If anyone would like to help me by translating the text of that game's tutorial, that would also be appreciated as it may help to clarify some rules.)

Thanks to Ed (who didn't provide his last name) for bringing George Hodges' leaflet to my attention.