Despite the kaleidoscopic magic ingrained in everyday life, Hitomi Tsukishiro's monochrome world is deprived of emotion and feeling. On a night as black and white as any other, amidst the fireworks spreading across the sky, Hitomi's grandmother Kohaku conjures a spell, for which she has been harnessing the moon's light for 60 years, to send Hitomi back in time to the year 2018 when Kohaku was in high school. Hitomi's mission seems unclear, but her grandmother assures her that she will know when she gets there. Following a trip through time aboard a train driven by a strange yellow creature, Hitomi finds herself in stoic artist Yuito Aoi's room, and his drawings flood her world with color. What is Hitomi's purpose there, and why do Yuito's drawings return such breathtaking color to her drab world?

Mahiru Shirota firmly believes that simple is best and troublesome things should be avoided at all costs. It is troublesome to do nothing and regret it later—and this ideology has led the 15-year-old to pick up a stray cat on his way home from school. As he affectionately names the feline Kuro, little does he know that this chance meeting will spark an extraordinary change in his everyday life. One day, Mahiru returns home to find something quite strange: a mysterious young man he has never seen before. His subsequent panic results in the uninvited guest being exposed to sunlight and—much to Mahiru's shock—transforming into Kuro! Upon revealing himself as a mere lazy shut-in vampire, Kuro promises to leave once night falls. However, one disaster after another leads to Mahiru accidentally forming a contract with his new freeloader, dragging him into a life-threatening battle of supernatural servants and bloodthirsty beings that is anything but simple. [Written by MAL Rewrite]

In the town of Kurouzu-cho, Kirie Goshima lives a fairly normal life with her family. As she walks to the train station one day to meet her boyfriend, Shuuichi Saito, she sees his father staring at a snail shell in an alley. Thinking nothing of it, she mentions the incident to Shuuichi, who says that his father has been acting weird lately. Shuuichi reveals his rising desire to leave the town with Kirie, saying that the town is infected with spirals. But his father's obsession with the shape soon proves deadly, beginning a chain of horrific and unexplainable events that causes the residents of Kurouzu-cho to spiral into madness.

Mio has feelings for her childhood friend Arata, but can't convey her feelings. One day, as they continue their delicate relationship, the two fight over something trivial. After letting tensions settle, Mio goes to make up with him in the pouring rain. While on her way, she gets into a traffic accident. When she regains consciousness, a mysterious and unfamiliar world appears before her eyes.