The Iron Tribe was allowed to make twelve of them, thus drawing a parallel to Heracles' Twelve Labors.

The Iron Tribe's contract goes as follows:

12 Labors

The 12 Labors as seen in episode 2.

  1. Treat your contractor as your King.
  2. To serve the King and never become one.
  3. Recover the homeland Earth to the hands of humans who are called the "Tribe of Iron".
  4. Fight against all survivors of "Tribe of Hero" and defeat every one of them.
  5. Secure the Mother Planet of "Tribe of Bronze" to the hands of humans.
  6. Secure the Mother Planet of "Tribe of Silver" to the hands of humans.
  7. Obtain the powers of "Tribes of Gold" to foresee the future.
  8. Obtain the knowledge of "Tribes of Gold" to generate Stars.
  9. To make humans who are called "Tribe of Iron" to become the master of universe.
  10. To protect the bonding party until these labors are fulfilled.
  11. To not to escape or to die until these labors are fulfilled.
  12. When these labors are fulfilled, humans also known as "Tribe of Iron" will make one contractor’s wish come true as long as such wish do not breach the other eleven agreements.

Note: The above 12 labors were directly translated in episode 2 of the anime -- the contract is meant for Age, the Nodos entrusted with protecting the 'Iron Tribe'.