K: The First is the adaptation of the 2012 anime K Project. Set in a world where history has taken a slightly different course from the one we're familiar with, K follows the story of a young boy, Yashiro Isana, whose life is caught in a psychic war between seven kings. Yashiro is an easygoing teenager content with just being a student, until his seemingly perfect life is halted when a bloodthirsty clan, glowing in red with fire, attempts to kill him in the streets. Unbeknownst to Yashiro, he is suspected of murdering a member of their clan and will need a miracle to escape their vengeance. Miraculously, a young man named Kuroh Yatogami swings in and aids Yashiro in his getaway, only to reveal he's also after Yashiro's life. Now a hunted man, Yashiro will have to evade the clans of seven powerful kings and desperately try to prove his innocence, before it's too late!

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.
(Source: September Scanlations)

Focused on Yata's and Fushimi's past. There are three parts: "Meeting," "Getting Along," and "Betraying."

The Green King surrounded by mystery, Hisui Nagare. Kurou's former senior disciple, Mishakuji Yukari. The youth who carries the weight being an executive, Gojou Sukuna. The drunkard and slovenly middle-aged man, Iwafune Tenkei. A manga depicting the daily life of the Green Clan, Jungle, with its abundance of personalities.

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 for them, their real target are...?

(source: AQUA Scans)

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.

(Source: ANN)

In Shizume city there's a legend about a red king with demon-like abilities that single-handendly created the Homra organization, as long as you get accepted into Homra, you can gain extraordinary powers.
(Source: AQUA Scans)