Midgar, all-girl academy, would have been notable just for the action of accepting its first and only male student, Yuu Mononobe. But Midgar stands out for much more than that: it's a school exclusive to a group of girls known as D's. Each of them have extremely powerful abilities in generating dark matter and manipulating it into powerful weaponry. The D's didn't exist twenty-five years ago, and only appeared after a number of mysterious, destructive monsters known as Dragons started appearing around the world. Strangely, just as suddenly as they appeared, they vanished. In their destructive wake, some girls started being born with symbols on their bodies and powers similar in nature to those wielded by the Dragons themselves. Now the D's attend this school, hoping to harness and utilize their powers against the Dragons. Yuu is their latest member and is extraordinary for being the only known male D in existence. Now he must forge relationships with the girls around him, including his long separated sister who attends the school as well, and work with them to investigate and eliminate the threat of the powerful Dragons.

It's been a year since the disappearance of Shiro, the Silver King; Kurou Yatogami and Neko have been diligent in their search, but to no end. Their investigation leads to a run-in with members of the now disbanded Red Clan HOMRA—Rikio Kamamoto and Anna Kushina—being pursued by the Green Clan, who desire Anna's powers for their own ends. Now, the members of Scepter 4 are called upon alongside Kurou and Neko in order to rescue Anna, the mascot, and only female member of the ruined Red Clan, from the enemy's clutches and hopefully find Shiro using the young girl's powers. Amidst crisis, the group is forced into a power struggle when the Green Clan threatens to overtake the Gold King's domain. The second step in the K Project series, K: Missing Kings, continues the story of a young boy caught up in a psychic war between seven kings, and showcases each character's struggles after the losses of their respective Kings.

The world we live in is called Earthside in this story. There are the other worlds called Nosfertia, Heavenstia, and Eternalia. When Darknoids from Nosfertia begun invasion to Earthside, Heavenstia sent 3 Animanoids (beast-humans) to prevent it. The lead character Touya had believed that he was a mere human but found he was actually a being of Eternalia. With the help of 3 Animanoids, Touya fights to defend Earthside.

Tensions are running high among the clans as the Green King begins making moves that threaten to drive the world into pandemonium. Following the death of the Gold King, the safety of the Dresden Slate, the source of power of the Kings, is under threat. Nagare Hisui, the sly and mysterious leader of the Green Clan Jungle, is determined to procure the powerful Slate by any means possible. Standing directly in his way is Sceptre 4, the Blue Clan, headed by their unyielding King, Reishi Munakata. However, the grim sight of his crumbling Sword of Damocles leaves the stability of his clan and all of Japan in jeopardy. Meanwhile, still recovering from their tragic losses, Anna Kushina and her aggressive clan HOMRA find themselves caught up in the Green King's games. Amidst the chaos, Kurou Yatogami and Neko are left vulnerable while their beloved friend, Yashiro Isana, the Silver King, remains missing. As the remaining clans struggle against the Green King's formidable forces, one final king appears.