The title of the manga can be translated as “one against 1,000″ or interpreted as “the strength to overcome 1,000″ but the manga and anime for Ikki Tousen is really just a crossbreed between Street Fighter and Romance of the Three Kingdoms.
The Romance of the Three Kingdoms is a lengthy historical drama regarding the “warring states” period of Chinese history. This was a time when rival warlords (princes, kings, sovereigns, whatever) were nearly constantly at war with each other. It was during this time that the writings of Sun Tzu were created, and the wisdom of Lao Tzu and Kung Fu Tzu took root in Chinese culture. Street Fighter, of course, is a video game in which contestants pummel each other with a variety of flashy karate maneuvers for no apparent reason.
A manga re-enacting the RotTK incorporating lots of flashy martial arts would be great (the Dynasty Warriors series of video games has attempted this). Ikki Tousen, however, takes place in modern Japan. The characters all conveniently have the same names as the generals and advisors from RotTK, and apparently are to varying degrees reliving the events of the ancient story. The Japanese versions of the names, of course, and instead of kingdoms these people are gangs that run some high schools.
The martial arts action is amusing, the character development largely accomplished by means of ominous summaries from the RotTK (e.g. “Sonsaku Hakufu was a great general reputed to…”) from the narrator. The character design in the manga is pretty good, though a bit heavy on the ecchi (can Hakufu have a fight without her shirt being ripped open? Not during the first few installments). The director of the anime clearly felt that showing off girls’ underwear was the primary reason to convert this story, and he does quite a lot of it.
I recommend Ikki Tousen for a quick read when you’ve got nothing better to do, and a reasonably good waste of hard drive space if you feel inclined to download it. You’re not going to be seeing any innovative characters, the depth of the plot is only “potential” at this point, and the potential is scarce (as of Episode 8 of the anime, or Volume 2 Chapter 6 of the manga), and technical merit of the animation team is mediocre. Note that this is produced as a television series, so they were operating under airtime deadlines. Cut the poor schmucks some slack when judging this one.