In Japan, there is a game called “shogi.” It’s a two-player strategy board game like chess, also known as Japanese chess or the game of generals, with rules that are pretty much the same as chess.
But there’s one significant and unique difference: you can use your opponent’s piece after you take it. The rule in chess is that after you take a piece, then that piece does not return to the board. I think this is a very interesting difference in the concept.
There’s a famous quote: “Yesterday’s enemy is today’s friend.” It means that circumstances can change, and even those who were enemies up until yesterday can become friends today.