After watching the anime more or less entirely for the opening sequence, I decided to give the manga a shot. I read all the way up to chapter 112, which was the most recent at the time, and haven't looked at TenTen since. I do read it for the story, but I view Oh! Great's potential as a writer with a certain skepticism.
The plot itself isn't particularly complex at any point in the story, but overall it struck me as inconsistent and convoluted in the extreme. The scope of the story and its themes starts out confined to that of a high-school martial arts manga (with the characters pondering the meaning of strength and why they fight), then expands during the Shin flashbacks to include the backdrop of the Takayanagi family and its strange ambitions, then suddenly balloons out to epic proportions as themes of fate, reincarnation, Japanese history, even more over-the-top supernatural elements, and obscure cultural references abound. (I read TenTen on onemanga.com - by this point even the translator has started to complain.)
It's not what's happening that's difficult to understand, but exactly why it's happening. Also, some of the character's actions just boggle me.
Spoiler (highlight to view)
Some things that I didn't quite get:
That white feather clan guy with the beanie and the mechanical arms. First he spends several chapters brutally (and without any particularly good reason) murdering people and ramming poles up their asses, letting his subordinates rape and torture the one vampire priestess he doesn't kill, and trying to kill his father and a bunch of other main characters. Then, after he's defeated and has somehow made peace with his father, suddenly he's the nicest guy in town, building mechanical arms for Souichiro's tragically handicapped mother and giving her limousine rides.
The past versions of Souichiro and Aya, and their comrades. Apparently they're the good guys, because the ruler they're staging a coup against is a warmonger and a douchebag of sorts, yet for some reason they seem to be always either killing people who don't have any clear connection to their goal, or torturing people unnecessarily (or both, as in the case of that little girl who worked in the brothel, whom they mindraped before stabbing in the head - why did they do that, again?)
Again, it isn't hard to follow what's happening, but at times I'm not quite sure why. I agree the story is deep, and has a lot of thematic undercurrents. But it just because it's profound doesn't mean it's a well-constructed plot. It's possible I'm just slow, and I'll probably read it again along with the latest chapters, but overall the story seems to have a lot of things wrong with it. I still enjoyed it, though.
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Allow me to reacquaint you with...
THE GROUND!