Source is rules found on pgs 16-17 of this document by Nader Daoud Daou (2007). Although this is the game from which modern Shogi is believed to have directly derived, the game are distinctly different if the following respects. Sho shogi has no drop mechanism. All pieces used in modern shogi are used in sho shogi and have the same movements and initial positions, but sho shogi also has one additional piece with respect to the modern game-- the drunken elephant which promotes to a crown prince and begins the game directly in front of the "king" (osho or gyokusho). The drunken elephant moves one space in any direction except directly backwards, and the crown prince moves exactly like a king because it is a second king. Namely both the crown prince and the king must be bared, checkmated and/or stalemated simultaneously to win. Baring counting as a draw only if one's own king can be bared the next move. According to "A World of Chess" by Jean-Louis Cazaux & Rick Knowlton (2017, ISBN 978-0-7864-9427-9), Bishop, Rook and Drunk Elephant were introduced to the 9x9 Shogi creating Sho Shogi, the immediate predecessor of Shogi, in the middle of the 15th century. Modern Shogi where created with the introduction of the drop rule and the removal of the Drunk Elephant piece in Sho Shogi. This happened between 1567 (Drunk Elephant still present) and 1587 (earliest recording of modern Shogi).