Original anime, produced by Sunrise, Inc.
Shown in online streaming site, Gyao (which, unfortunately, you can't access unless you are on Japanese server)
Official website:
http://www.irohanihoheto.jp/What it's about: 17 year-old Youjirou Akizuki is an Eien no Shikaku (Eternal Assassin), who has a sword called Getsuruitou (Sword of Moon Tears) and has a task of finding and destroying Hasha no Kubi (Conquerer's Head). That's the main, most basic plot of the anime, but a whole lot more goes on.
http://en.wikipedia.org/wiki/Bakumatsu_Kikansetsu_Irohanihoheto Go there to get some more ideas about it.
There' are lots of historical stuff (and people) mentioned throughout the anime. And the quality the animation changes from episode of episodes due to change in animation directors and sometimes outsourcing of the episode. (to save on budget)
I've been literally obsessed with this anime. I don't think I've been this obsessed on any other anime(manga is different story, lol *cough*Tsubasa*cough*).
Check out the OP of this anime on youtube too.... the song is awesome ^_^ (it's Kouya Ruten by FictionJunction Yuuka)
I recommend it ^_^
Anyone already watch it by any chance?