Tenjiku

Tenjiku was a gang organization in Yokohama led by Izana Kurokawa.

Leader
Izana is Tenjiku's supreme authority as well as its pillar.

Four Heavenly Kings
The Four Heavenly Kings are the four strongest fighter's in Tenjiku. It is unclear if they have the same functions as Toman's Division Captains, but it is heavily implied so, as the Four Kings all appear with their corresponding squads, and one of them (Ran Haitani) even has his own second-in-command (his brother, Rindo Haitani)

General Chief of Staff
Tetta Kisaki's position. It is unclear what are the functions of this position, and where it falls on Tenjiku's hierarchy, but it clearly involves a lot of power, and allows Kisaki to give orders to any Tenjiku member other than the Executives. It is heavily implied that the position was made just for Kisaki after he became an ally to Izana Kurokawa.

Executives
Theoretically, any upper echelon member is considered an "Executive". There is, however, a member of Tenjiku that is refered solely as "Executive", that being Yasuhiro Muto. It is unclear why he lacks a more specific title, but it is heavily implied that's because he couldn't reveal himself as a Tenjiku member until near the final battle, in order to spy on Toman from within. He is also informally recognized as one of the Four Heavenly Kings after Shion Madarame's defeat.

Etymology

 * Tenjiku is the Japanese terminology for Tianzhu (derived from India's Sindhu) as referenced in Journey to the West, the story from which Izana drew inspiration to build his kingdom.