Thirteen Night Swords

Thirteen Night Swords (十三の夜剣) is a secret society formed by thirteen major aristocratic families who covertly maintain great influence over the Midgar Kingdom with help from the Cult of Diablos.

Overview
The Thirteen Night Swords are an underground faction within Midgar Kingdom that secretly control the nation. The organization possessed immense wealth and control many territories within the Kingdom. Due to their aristocratic status, the members of the organization can abuse their authority without any repercussions allowing them to commit any crimes while leaving unpunished.

Membership
The Thirteen Night Swords are a group of corrupt nobles, comprised of thirteen great noble families who banded together and formed an alliance to which they swore loyalty to the royal family while, in reality, secretly engaging in power plays.

Trivia

 * Isaac's family is presumably a member of this organization.