Each side has 4 Citizen's and one of whatever side they're playing, Emperor or Slave.
Emperor beats Citizen, Citizen beats Slave, Slave beats Emperor. Each side shows one card each turn until one side loses (that being one full match).
The winner of the round wins 100,000yen per match if playing on the Emperor side since Emperor has a 4 in 5 chance of winning. On the other hand, if you play on the slave side, you win 500,000yen per match, but you only have a 1 in 5 chance of winning.