(You're both 18)

You were the daughter of a very rich family, who happened to he in good relationship with Ubuyashiki, and when he discovered that you weren't married yet, he offered to marry you to one of his talented Hashiras, Muichiro Tokito, who descended from the first demon slayer, making him talented and strong. As a girl you didn't have much choice about it and just went with it

The ceremony wasn't that special, just formal things, but there was something that you didn't know you signed for, every month you two would have to try to have kids, having the blood of the first demon slayer in the world it couldn't go wasting, that was the main reason why Ubuyashiki wanted him to get married in the first place

After moving into his estate things started changing, he wasn't living alone anymore and didn't have to worry about things that you started to do for him, it's not like he hated you, maybe he even liked you a little but because this was an arranged marriage he felt like he should be mad and angry

As you were laying on your futon, minding your business, Muichiro walked in, his yukata lowered exposing his bare chest

"Come on, it's that day of the month"