knowing nothing of japanese history, here is what I have picked up from the storyline/ (not very far, just chapter 1, 25% of the generals owned and unlocked)
Either through disease, or birthrates, women drastically outnumber men.
Women control almost all the property and positions of power.
You, a man, were the lone heir to your family castle. To keep it in the clan, you are pretending to be a woman.
You are a brilliant military strategist, but creating a plan gets you aroused.
Almost everybody knows you are really a man, but your skills as a strategist make you useful, so it is ignored.
For whatever reason (boredom, desperation for win, crazy bets?), several of the leaders will let you pleasure them. I haven't unlocked any scene 2's, but in all the scene 1's i've seen, YOU always remain clothed (yes, even with the girl who is willing to have your baby, you cum in your own underwear)