What Is Fairy Tail Zero?
The founding of the guild, told by Mashima himself in a single volume.
Fairy Tail Zero is the prequel Mashima drew to his own series: the story of Mavis Vermillion, the first master of Fairy Tail, and of the guild's founding a century before Natsu's time. It ran monthly from July 2014 to July 2015 in Monthly Fairy Tail Magazine, a magazine Kodansha created for the franchise, while the main series continued weekly.
Where the spin-offs were delegated to other artists, Zero was kept in-house: it is the only Fairy Tail side story of its era written and drawn entirely by Mashima, and it answers the main series' oldest question, where the guild came from, in one collected volume.
THE PREQUEL, DOCUMENTED
Monthly Fairy Tail Magazine · 2014–2015A magazine of its own
In 2014 the franchise was given a monthly magazine, Monthly Fairy Tail Magazine, launched July 17, 2014. Mashima used its first issue to begin Fairy Tail Zero, drawing the prequel himself in parallel with the weekly series, which at that point was in its eighth year.
Thirteen issues
The magazine ran for exactly thirteen issues, ending July 17, 2015, and Zero ended with it. The complete prequel fits inside that single year of monthly chapters and was collected as one volume.
What it answers
Zero is set in the year X686, a century before the main series, and follows Mavis Vermillion, the guild's founder: how she learned magic, how she met the treasure hunters who became the guild's first members, and how Fairy Tail came to exist at all.
In English
Kodansha USA announced the prequel in November 2015 and published it as a single volume, keeping it the most self-contained Fairy Tail book in either language: one volume, one complete story.