Each tribe who possess one or more Nodos is allowed to make a contract with them. They can draw specific amount of clauses, called Labors, this amount was determined beforehand by the Golden tribe. The Iron tribe was allowed to make 12 of them. The Silver tribe, still unknown about how many Labors there are.
The Iron tribe's contract goes as follows:
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 "Iron tribe".
4. Fight against all survivors of "Heroic tribe" and defeat every one of them.
5. Secure the Mother Planet of "Bronze tribe" to the hands of humans.
6. Secure the Mother Planet of "Silver tribe" to the hands of humans.
7. Obtain the powers of "Golden tribe" to foresee the future.
8. Obtain the knowledge of "Golden tribe" to generate Stars.
9. To make humans who are called "Iron tribe" 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 "Iron tribe" will make one contractor's wish come true as long as such wish do not breach the 11th agreement.