Alternate history is full of possibilities for fiction; a writer can change the world without going into the genres of fantasy or sci-fi, turn cultures on their heads, made political commentary without using an existing political system and pissing people off--or, in the case of Ooku, just tell a hell of a story.
In Ooku three-fourths of Japan's men have been killed by a virus, and so women take over while men are pampered and protected as delicate seed-bearing treasures. Though Yoshinaga could easily have used this premise to create porn, she avoided the temptation. Instead, the men in her story go through what women in history did: they have no say in their marriages, are often sold to brothels, and are granted little freedom in public life.
Our hero, Mizuno, through a fascinating set of circumstances I won't spoil here, winds up serving in the new Shogun's harem of beautiful men. Again, it's a premise that screams "porn" that Yoshinaga skillfully weaves into a narrative of politics, friendship, and intrigue as Mizuno, a simple country bumpkin, realizes how hateful the Ooku, or Inner Chambers, are. It's full of hundreds of men all competing for the Shogun's attention, and like harems of women in history, they're willing to do whatever they have to to climb over each other to power. Meanwhile, the new Shogun is a simple woman who dislikes luxury and is all about cutting costs and increasing efficiency. While Mizuno is wrestling his way through backstabbing, murderous men in the Inner Chambers, the Shogun is trying to wrangle respect from a court that demands extravagance in a time of poverty...and from foreign dignitaries who have never seen a female ruler, who will mark Japan as weak and ripe for conquest should she misstep.
There's a lot of unconventional bits to this manga. While manga characters are usually teenagers, the cast of Ooku is (mostly) adult, with many characters in their thirties and forties. Manga is often a quick read, but Ooku had plenty of dialogue and story, and took time to get through. I finished feeling like I'd read something, and when I read it again, because I'm sure I will, I'm positive I'll discover new things I missed before. The history is also accurate, deviating only with the number of men and women and their roles. The art is quite simple, perfect for the real-world setting and realistic atmosphere Yoshinaga was obviously going for.
The unrealistic part comes in the two main characters. Court life in any country beat the soul out of anyone who tried to be nice, but here Mizuno wins friends with his honesty/forgiving nature and the Shogun gets away with massive changes that inconvenience her court even though she's kind enough to do some very giving things. People like that would have been eaten alive in real history. I understand why Yoshinaga chose to write characters like them; a lot of readers want people to like and relate to in their fiction, and realistic protagonists couldn't have been likable. I'll chalk them up to artistic license, and since I did like both, I'm not complaining, just noting.
Overall, Ooku is intelligent, original, weighty without being depressing, never preachy, and as well-put-together as I've ever seen a manga be. It should be interesting to history fans, but also to people interested in anthro-soc topics as a gender switch story like this has as much to say about modern ideas as it does about historical ones. I can't wait for future volumes.