Taikyoku Shogi is the largest known Shogi variant, with 804 total pieces on the board. It is first documented in Japan in the Shogi Zushiki, which is reportedly from the seventeenth century.
Rules
Taikyoku Shogi's rules are similar to that of Shogi, but are expanded, with many types of pieces with different movements. The full suite of movements are listed here: Wikipedia
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