Grimoire Heart

Grimoire Heart (グリモアハート Gurimoa Hāto 悪魔の心臓 lit. Demon's Heart) is one of the three Dark Guilds that comprise the Balam Alliance, as well as the strongest Dark Guild.

Goals
When they are first seen, Grimoire Heart's goal is to acquire all the keys that could unlock Zeref's seal; they have finished acquiring all the keys and are now aiming to locate him, physically capture him and bring him to Hades, and bring him out of his slumbering state. Now that he has been located they have the intention of using him to rule a world (called "The Ultimate Magic World") where the 90% of the world's humans that cannot use magic will not be able to survive. Caprico later reveals that another one of Grimoire Heart's goals is to destroy Fairy Tail.

Location and Buildings
Grimoire Heart doesn't seem to have any stable localization. Its members live and travel on a giant airship that flies high above the land. Because of this, it is an elusive guild.

This airship has heavily reinforced plating and is equipped with a version of the Magical Convergent Cannon - Jupiter. It also houses the Devil's Heart - a generator like machine that serves as both a power source for the Guildmaster as well as life support. Despite its large size, it is quite fast and maneuverable, as it was seen dodging a punch from a gigantic Makarov.

History
What is known of this guild is that its current guild master, Hades (real name Purehito), was the second guild master of Fairy Tail. However, 48 years ago, he bestowed the guild master title on to Makarov so that he could go on a journey. On this journey, Hades traced back the origins of magic to Zeref, where he saw what can be called the "essence of magic". It is assumed that he turned "evil" after this point, and that he created Grimoire Heart and became its guild master. Hades later revealed that he spent years raising the Seven Kin of Purgatory and that they are his greatest mages who use magic that is as close as possible to the source of all magic: Lost Magic.

Strength
As a member of the Balam Alliance, Grimoire Heart is one of the three most powerful dark guilds. In fact, it is stated to be the strongest dark guild by Levy and one of the three greatest protuberances of the magic world (alongside Fairy Tail and Zeref) by Lahar. Unlike the Oración Seis, Grimoire Heart has far more than six members, having several core members as well as numerous members of lesser rank. Many of its core members have been shown to be incredibly powerful, and when they arrived to fight Fairy Tail at Tenrou Island they manage to battle and even defeat some of Fairy Tail's core members. Its strongest member was able to fight on almost equal grounds with Gildarts Clive, and every member of its strongest team (The Seven Kin of Purgatory) have proven themselves to be S-Class strength. Some of them even managed to combat powerful S-Class Mages such as Erza Scarlet and on equal grounds. Although with 3 of their members deceased including the Guild Master, 2 (technically 3) of their members defected, and with 2 of their strongest members no where to be seen Grimoire Heart's strength has lowered significantly.