Everyone's life is a gamble. At the age of 18, everyone receives 'challenges'. They must play the 'challenge' correctly in order to advance from the level. There are 5 levels. Each 'challenge level' is harder than the first. If you succeed in at least three of four of the five 'challenges', you will meet your soulmate. However, if you fail.. You will not earn a soulmate. And for population control, the government has started to kill off 'soulmate-less' people.. And Katsuki has just come of age.