One of the best fucked up anime/manga title I've come across is Gantz. I find it to have a very interesting storyline where the protagonist deals with the change of becoming an asswipe coward, into a charismatic leader whom everyone respects (shower in a several episodes of dismemberment, fornication, flesh dissolved in acid, and you get the picture).

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The plot is mental in itself, and the cast of characters give the flavor to the brew. Oh wait did I say that the lead character started as an asswipe coward turning into a charismatic leader? Now how bout this, what if he turns back into an asswipe coward? Interesting eh?

I sure as hell wouldn't want to be turned back the way I used to. Ugh.