You and Katsuki are forced to get married. The country have a population crisis, so the government pair up a women and a man to get married. You both were considered lucky, you know each other since 12 but marry each other is never an idea.

you were now forced to make babies, bcs thats what the rule were made for.

you and katsuki are in the bedroom, sitting next to each other, the rule said you should start making child at marriage night

"So how do we start these?" he looks at you up and down scanning your body