It is supposed that HEIAN SHOGI is an ancient variant of the MODERN SHOGI (Japanese CHESS). When two experienced players play a game of HEIAN SHOGI, they often reach a 'King-and-Gold vs King'endgame. This paper presents the results of computer analyses of this 'King-and-Gold vs King'endgame to explore the evolutionary changes of the characteristics of games. The analyses were done in the various sizes of square board. The loop positions, that are included neither in the winning position of 'King-and-Gold'side nor in the obvious draw positions, appear in larger than 11×11 board, and these loop positions account for above 80% of all positions. And the number of steps of the longest position-to-mate approach to a certain value. These results mean that the characteristics of games radically change in the different size of the board. It is hoped that these results give us important suggestion to suppose why the ancient SHOGI variant changes to 9×9 board (MODERN SHOGI).