Junto Nakano was a normal high school teenager. That all changed when one day, while walking home from school, he stumbled across a pack of cards for a card game called ‘Killjoy’. Most people dismissed this as an urban legend and Junto thought nothing of it until he discovered another Killjoy player and challenged them to a battle. Junto realised this game was messed up when his opponent played a card with the effect ‘Your opponent can’t breathe until they end their next turn’ and Junto finds himself gasping for air.