The Echelon

The Echelon (エシェロン, Esheron) were spiritually aware beings who resided in the Soul Society before the First Shinigami-Arrancar War.

Origin
During The Wandering Clans Era, the Echelon resided in more developed areas of the current Rukongai. They were primarily noble merchants, selling to nomads and selected clans in order to gain a profit. Their patriach, Shūshi Musokuno Kaenōra, perfected the art of Reiseī, allowing his people to unite as one culture and promote learning.

Influence in the First Shinigami-Arrancar War
The Echelon were taken in as loose allies of the Shinigami seeing as both were being attacked and killed by the Hollows. However, the members of the Echelon were not impressed by the way the Shinigami's way of handling their men, citing Hikaru Kurosaki and Seireitou Kawahiru as their primary targets of revulsion.