Legacy Unbound (AoT/Blue Exorcist crossover fanfic)

While on a mission with Levi, Eren,and Mikasa, Armin is eaten by a Titan. But he is then saved by Mephisto, who takes an interest in the little blonde boy for he believes Armin has an untapped power. Mephisto offers Armin a chance to become stronger by becoming a student at True Cross Academy and learn the ways of an exorcist. Armin accepts his offer and lands in the world of Blue Exorcist. Armin meets Rin and the gang, then joins them on their missions.

Join Armin as he learns to become an exorcist at True Cross. And learn how to harness his own strength.

But what is Mephisto's real purpose for taking Armin into True Cross? What other secrets lurk about Armin's true heritage? And what legacy will be uncovered?