The story takes place in modern day Japan, not too long after WW3 happened- women took over the Japanese government and now ask for men to rap battle each other to entertain them and to earn money and fame. ... Yeah, that's the shortest and sweetest way I can sum up the backstory.
There's six main division with three members each- each divison coming from and representing a part of Japan. Buster Bros!!! (of Ikebukuro), Mad Trigger Crew (of Yokohama), Fling Posse (of Shibuya), Matenrou (of Shinjuku), Bad Ass Temple (of Nagoya) and Dotsuitare Hompo (of Osaka) are all participants of the Division Rap Battles. Most recently, the Party of Words (of the central government, Chuohku) are also particpating.
ABRIDGED CHARACTER DESCRIPTIONS
Special shoutout to PokeyDokey, Mayhem, and everyone else in the WTTD server for helping me write these.

Known as "MC Big Brother", Ichiro is friendly and helpful to almost everyone, but especially his two younger brothers. He runs an Odd-Jobs shop in Ikebukuro. He has a love for anime and manga. I think he'll literally explode if he isn't shouldering twelve burdens at once.

Known as "MC Middle Brother". Jiro is a high school student that is easy to get along with- though he's quick to anger when someone disrespects his brothers. He frequently beefs with Saburo, usually being teased by the younger for not being as book-smart as him. Jiro's a sweet boy, it's like having a pomeranian as a guard dog. He also likes soccer, that's his one non-brother related interest.

Known as "MC Little Brother". Saburo is a middle school genius, and he has no problem with looking down on people he considers beneath them. He's not the greatest at socializing, but he respects his older brothers greatly (even if he doesn't admit it to Jiro's face often). Has developed a bit of a god-complex, because middle schoolers just be doing that sometimes.

Samatoki is the second in command of a yakuza family and knows how to come across as rough and intimidating. Underneath that, he cares very deeply for his family and comrades, though he may have a hard time showing it. Also, he will NOT eat his vegetables.

A police officer who despises drugs, but is willing to overlook nearly any other crime as long as he gets something out of it. He usually speaks in a calm, almost condescending manner, that makes you want to punch him in the face but you CAN'T because he's goverment property. He canonically owns dozens of pairs of glasses on display in his room.

A former soldier in the navy, currently living his life in the woods using his learned survival skills. He's usually level and deadpan, not one to outwardly express his emotions (Although he isn't aware of this, and believes himself to be plenty expressive.) He has an unyielding loyalty to his friends, and would absolutely die for them. He's an extremely talented cook, and loves to share his cooking with others. Unfortunuately the ingredients are whatever he finds in the forest, and can be rather... unconventional.