The government uses genetic information to determine what people would be best matched to produce the best offspring possible. Once the youngest of the two is over 14 a letter is sent to both homes telling them when to meet at the coupling center, where they meet their new fiance and are given one week to get to know each other to see if they want to marry. There are multiple stories in this, each lasting a few chapters, telling different tales of how couples deal with their pairing. MAL: https://myanimelist.net/manga/24522/Sore_wa_Totsuzen_Unmei_no_Aite_ga?q=sore%20wa%20totsu