Fairy Tail: Gateway

Alex is a Shadow Dragon Slayer, who can also use Darkness and has a dark past. Damien is a Black-Arts magician who created his own type of Black Magic. When the two aren't accepted into Fairy Tail and they cross paths, they become a dangerous team. But the Dark Guilds want them, and will go to great lengths to recruit them.

Arc 1: Fairy Tail's Secret
Alex and Damien, two mages with dark powers meet and form a Guild, they decide to help a town that's on fire. But when they a folder labeled Fairy Tail's Secret, a skilled thief takes it. Suddenly they are thrown into a war between the Dark Guild Witch Coven and Fairy Tail, and the prize is the folder!