The basic concept of Ikkitousen is that in modern day Japan several students inhabiit the reincarnated souls of ancient warriors. Because these are souls of warriors that fought over 1800 years ago these students are now fighting each other nearly to the death. Essentially Ikkitousen is about these students trying to either fight the destiny of the souls they inhabit or making that destiny come to pass.
The main charaacter of Ikkitousen is Hakufuu who is rumoured to be the reincarnation of a legendary fighter who was supposedly known for defeating many opponents with ridiculous ease. Hakufuus best friend is Koukin who is trying to help her restrain her power and energy lest she become a mindless villian once her true power is released.
The art in Ikkitousen is simply superb and very easy on the eyes. The backgrounds look good and the movements are fluid and lithe. While im on the visual aspect of the show this might be a good time to mention the fan service. There's alot of dialogue about the "big O" and comments on whether some of the characters have ever f*cked before or not. Add to this the overwhelming amnount of fan service that this show offers. Hakufuu often leaves a battle with a mere fraction of the clothes she was wearing when the fight began. All this fan service sometimes overwhelms the fact that this is a show of the fighting genre.
The fights themselves are pretty good with plenty of reversals punches and kicks and the like, but sometimes the fights are just power hit versus power hit And there's plenty of blood flying around in this show too. Alot of shows just have loads of fighting but no blood. Depending on what you like this show is really a love it or hate it anime.