[Demon Slayer] Marry the Winner of Life

[A short story about still Yuanyi, still getting married but the heroine becomes a sister] You have traveled through time to the Warring States Period in Japan, which was at least 500 years away from a tragic death. The daimyo's biological father is seriously injured and on the verge of death. There is no male heir in the family, so you are faced with the problem of recruiting a son. The good news is, you found that invincible man! The bad news is, the invincible man is now 7 years old(.) *Single Demon Slayer, background of the Warring States Period, the only daughter of the heroine's daimyo, Yuichi is the son-in-law, and she is raised in the family *Second person third person interspersed, the heroine is older, the age difference is 8, there is no emotional line before the two adults *The update of the rehabilitation article is unstable and has no outline. It is very short. How can it be delayed no matter how unstable it is? Purpose: Love makes people better