By Japanese author Koda Rohan, from his essay collection Shogi Zatsuwa, section 4, 「玉将につきての俗説」 (“Folk Beliefs About the King Piece”). This short essay discusses traditions around the shogi king.
Folk Beliefs About the King Piece
In the so-called “Bantarō” shogi pieces, one of the two king pieces is marked 玉, but the other is marked 王. Because of this, some people say that when you sit down to play, good manners means giving the piece with 玉 to the more honored person. I would say that is not worth taking seriously.
Still, maybe writing one as 玉 and one as 王 is not new. A book called Ainōshō, made in the Bun’an era, is said to talk about shogi pieces and to say this: writing one as 玉 and one as 王 is done because people think it is bad to have “two kings in one country,” and that this is something calligraphy families pass down by word of mouth. I have not seen that book myself, but I would call it a questionable and foolish story.