The main character is Nick Brown. In many 'gangsta twilights nick brown fanfiction' stories, he is portrayed as a complex character with his own motives and goals in the darker side of the Twilight world. Other characters can vary widely. Some might bring in the Volturi as a sort of overarching power that Nick Brown has to deal with, while others might focus more on his interactions with the werewolf packs or other human characters in a more gangsta - inspired way.
Typically, Naruto in a 'gangsta naruto fanfic' is a tough and street - wise character. He's not the naive kid we see in the original. He has a bit of an edge, using his natural exuberance and ninja skills to navigate the rough world he's in. Sasuke might be a brooding, more mysterious figure, perhaps with his own hidden motives within the 'gangsta' setting.
Well, the Gangsta manga ends with a mix of closure and ambiguity. Some characters get the resolutions they deserve, but there are still elements that make you think and wonder about the future.
It could mean that there is a fan - created story (fanfic) about Naruto where the characters are depicted in a 'gangsta' - like style. For example, they might have the attitude, appearance, or behavior associated with gangsters in a modern or unique setting within the Naruto universe.