Soul Eater primarily revolves around students known as meisters (職人, shokunin) or technicians at the Shinigami Weapon Meister Vocational School (死神武器職人専門学校, Shinigami Buki Shokunin Senmon Gakkō, or Shibusen (死武専, Shibusen) for short, located in Death City. The school is run by Shinigami, the God of Death himself, as a training facility for weapons created by shinigami and the human wielders of those weapons, the meisters.

Each meister has at least one weapon companion which has both a weapon and human form. Shinigami created the school as an organization that enforces peace in order to prevent the rebirth of the "kishin", evil demon gods that nearly destroyed everything by plunging the world into chaos. Human souls that have become evil by straying from the path of humans have a high risk of becoming kishin, so evil humans are constantly being hunted down and killed by the students trained at Shibusen. The ultimate goal of the students with their weapons is to have their weapons defeat and eat the souls of ninety-nine evil human souls and one witch's soul which will dramatically increase the power of the given weapon and thus be capable of being used by shinigami.

From Wikipedia.org

SOUL EATER. HIS FRIENDS...CALL HIM SOUL.
THE ULTIMATE PRIZE...SOUL EATER.
YOUR SOUL IS GONNA BE MINE!