Also, I believe this is a reference to the Momiji article in Symposium of Post-Mysticism which discusses Momiji (and other youkai) creating new pieces for their games:
"Pieces which have been currently found include the "general", "lieutenant general", and other such pieces, which supposedly are promoted versions of pawns. There were also pieces like "airplane" and "spy", whose effects are truly unimaginable.[8] There was nothing written on the backs of any of these, which means they can't be promoted.[9]"
It's a piece of a special military shogi, unlike the Tengu (that Momiji seems to be pioneering in that article) aimed to be fast, so no promotions, and the pieces were military themed. There are a lot of different types of Shogi, being the main ones regular Shogi and Dai-Shogi (Big Shogi: larger board and a lot more pieces; it also takes a lot more time to finish one game).