Set in the Shinigami technical school for weapon technicians, the series revolves around three pairs of two characters with each having a weapon technician and a human weapon. They try to make the latter a "Death Scythe" and thus fit for use by the Shinigami. They must collect the souls of 99 evil humans and one witch to do this.

Note: There were two versions of Soul Eater. The first was a normal version which aired on Mondays and the second was a "Late Show" version which aired on Thursday nights. The "Late Show" version had some extra scenes added during eye-catches and before the next episode preview but the main part of the show didn't have any differences from the normal version.

[Source: AniDB]

Soul Eater Not! is a side-story to the main series, focusing on a freshman halberd named Tsugumi Harudori, who befriends two other meisters, Meme Tatane and Anya Hepburn. All three take part in the NOT (Normally Overcome Target) class at DWMA and learn to control their powers in order to overcome their difficulties to have a normal life, as opposed to the battle-oriented EAT (Especially Advanced Talent) class taken by Maka, Soul, and their companions.

[Source: Wikipedia]