The Race Piece (種のコマ, Tane no Koma)? is a chess piece bestowed upon the representative leader of each race. The Imanity own the King, the Flügel own the Queen, the Elves own a Rook, the Werebeasts own a Pawn, and the rest have yet to be revealed. It is later revealed that, by conquering all the Exceed races, and thus having all the 16 chess pieces, one attains the right to challenge Tet for the title of One True God. As all the 16 Race Pieces are needed to have a full chess board that you need to challenge Tet. Tet did not create the concept of the race pieces, Riku and the "179 Ghosts" of Imanity did.
The Race Piece holds the rights of the race they belong to, so while the Races Pieces can be bet, it is unwise to do so. If a races representative bets their race's Piece and loses, the races rights as an Exceed are stripped and the pledges no longer apply to them. Hence no one has ever bet their Piece in the past, Sora being the first one to do so.
Sora was the first representative to bet his race's Piece, and after winning, he is also the first to succeed in holding on to it.