and its R18 side-story Life Exchange http://novel18.syosetu.com/n3670da/
His writing style is quite friendly with machine translator. I read almost all it with Machine Translator one-by-one sentence
Protagonist is military-man and young head of low-tier aristocrat family
that want to offer his little sister to be one of many emperor wife, So his family could have better status.
But little sister is not willing
so they have argument and have accident that cause them to swapped.
Protagonist now have to enter the castle in place of his sister.
The emperor himself actually is misogynist, even he have almost hundred wife, he never lay his finger to any.
Protagonist identity was revealed to other wife and emperor early on story.
[spoiler:lit]Since protagonist revealed himself to the emperor as man,
and give good political and war opinion to emperor, he is liked (not love) by emperor and have to giving his virginity to the emperor.
He is not like having sex with man, but as for people in this story POV, is logical to obey and giving anything to the emperor.
After that, he is pregnant emperor son and is appoint to be empress.
Later on with story going, the empire itself is having war and is in bad condition, empire need to ask for help from one tribe
which have ugly look. the price is that almost all of people in empire was swapped. Including emperor himself losing his body
to leader of that tribe and beatiful princess with that tribe military man/empire military man.
The story is focusing on what is actually identity of human. soul or body and diffence between man and woman both mind and physically.
Ex. the reason that most of empire military man was swap to woman is because woman body will have a low ambitious so, it can prevent coup.
The side story is a POV of swap in difference situation and result, focusing on role, place, status of people with sexual element.
Even with machine translation result, I can fap to this.