In modern Japan there are seven "Kings" who share power with their fellow clansmen. The Blue King Reishi Munakata, the leader of the Blue Clan "Scepter 4," held great responsibilities on his back. The tower that Gold King Daikaku Kokujōji supervised called the "Dresden Slate" was still on his mind, and he felt a great burden by killing the previous Red King, Mikoto Suoh. On the other hand, the former Red Clan "HOMRA" clansman Anna Kushina experienced the attacks from the Green Clan "Jungle" and awakened as the next Red King. By doing this, she bound her comrades through a strong bond once again. Finally, White Clan members Neko and Kuroh believe that the White King Yashiro is still alive, and seek his whereabouts. However, it was not just them searching for the White King. With "Jungle" once again jumping back into action, the fates of the various Kings are brought together.
from ANN

From September Scanlations:

Yatogami Kuroh has lost the only thing remotely close to family he had left—and to make matters worse, he’s been charged with a final task by his master that he isn’t entirely sure he’ll be able to fulfill. Follow this young modern-era samurai as he sets off on a quest to track down the next Colorless King and determine if he’s evil or not…and to strike him down where he stands if he is. (Off-shoot manga of the anime ‘K Project’)

From AQUA Scans:

Tokyo Regional Legal Affairs Bureau Census Division, Annex 4, also known as SCEPTER 4, is a police institution that aims to stop criminals with special skills. But their real target is...?

Set in a world where history has taken a slightly different course from the one we're familiar with. In Shizume City there is a psychic war between seven kings. The story goes that the Third King, known as the Red King, created a group called HOMRA filled with extraordinary people. If you manage to join HOMRA, you also acquire unbelievable psychic abilities.

Shiro and Kuroh are not the only ones who go to high school. Instead, the members of Homra (including their leader Suoh) and the members of Scepter 4 attend school together. The students are sometimes lax, but at other times, they are hot-headed.

The story takes place in a world where seven people with unusual powers are crowned as "kings," and revolves around the "bonds" and "fate" between the people involved.

This is the story of how Yata Misaki and Fushimi Saruhiko met, became fast friends, and, eventually, parted ways.

manga sequel to K project movie, Missing Kings.

The story of the Green Clan, "Jungle," starring antagonists of K anime series 2, K: Return of Kings.