The father's remarriage was suddenly announced without any consultation. Kosuke' suddenly finds himself living with his sisters-in-law. The two sisters are very close and have opposite personalities, one of them is a bright and mature 'Kana' who calls herself 'big sister' even though she is younger than 'Kosuke'. The other is the withdrawn 'Sayo', who hates men and only shows her grumpy face to 'Kosuke'. And without caring about my sudden confusion, the father moved to a new house with his new wife just one month after they moved in together. As a result, 'Kosuke' was left to take care of the two of them. Fortunately, the sisters seem to get along well, so 'Kosuke' should only manage the money that is sent to him and do the housework. He decided to live peacefully. And in the morning after a few weeks of living with the three of them, I wake up in the same bed as one of my sisters-in-law 'Kana'.