K unfolds in a world where the Kings are rare individuals who wield extraordinary supernatural powers, gather followers into color-coded clans, and bear responsibility for the lives and honor of those who serve them. In technologically advanced Shizume City, ordinary Ashinaka High School student Yashiro Isana is living an unremarkable life when a video showing the brutal murder of a Red Clansman spreads across the city and leaves him accused of homicide. A manhunt begins for his head, drawing him into the orbit of Neko, Kurou Yatogami—the infamous "Black Dog," a skilled swordsman and martial artist who is still determined to honor the final wishes of his late master, the Seventh King—and the rival factions surrounding Red King Mikoto Suou and Blue King Reisi Munakata.
As Yashiro struggles to prove his innocence, clouds begin to appear in his memory, even close friends start to question his very existence, and a larger conspiracy starts to surface behind the scenes. At the same time, Mikoto Suou is drawn toward his own imminent fate. What first seems like a simple murder case expands across the K franchise into a broader conflict between Kings and their clans, including Mikoto's HOMRA and Munakata's Scepter 4. With loyalties splintering and old grievances sharpening, the search for the truth pulls Yashiro toward the center of a power struggle that could ignite a full-blown war between Kings, with the fate of the world hanging in the balance.