Shizuku Tsukishima is an energetic 14-year-old girl who enjoys reading and writing poetry in her free time. Glancing at the checkout cards of her books one evening, she notices that her library books are frequently checked out by a boy named Seiji Amasawa. Curiosity strikes Shizuku, and she decides to search for the boy who shares her love for literature. Meeting a peculiar cat on the train, Shizuku follows the animal and is eventually led to a quaint antique shop, where she learns about a cat statuette known as The Baron. Taking an interest in the shop, she surprisingly finds Seiji, and the two quickly befriend one another. Shizuku learns while acquainting herself with Seiji that he has a dream that he would like to fulfill, causing her dismay as she remains uncertain of her future and has yet to recognize her talents. However, as her relationship with Seiji grows, Shizuku becomes determined to work toward a goal. Guided by the whispers of her heart and inspiration from The Baron, she resolves to carve out her own potential and dreams.

Many years ago, after the end of a bloody world war, mankind took shelter in six city-states that were peaceful and perfect... at least on the surface. However, Shion—an elite resident of the city-state No. 6—gained a new perspective on the world he lives in, thanks to a chance encounter with a mysterious boy, Nezumi. Nezumi turned out to be just one of many who lived in the desolate wasteland beyond the walls of the supposed utopia. But despite knowing that the other boy was a fugitive, Shion decided to take him in for the night and protect him, which resulted in drastic consequences: because of his actions, Shion and his mother lost their status as elites and were relocated elsewhere, and the darker side of the city began to make itself known. Now, a long time after their life-altering first meeting, Shion and Nezumi are finally brought together once again—the former elite and the boy on the run are about to embark on an adventure that will, in time, reveal the shattering secrets of No. 6.

All his life, Yuuya Tenjou has been the subject of resentment and contempt from everyone around him, even from his parents. To make matters worse, his grandfather—the only person who ever showed him affection—suddenly dies, leaving Yuuya truly alone. Despite facing many adversities, Yuuya does what he can to offer kindness to those who need it—but even the most good-natured people can only tolerate so much abuse. Just when he reaches his breaking point, a flicker of hope appears in the form of a hidden door in his bathroom. This door provides two-way access to an abandoned house in another world, where he instantly gains game-like stats and skills. Moreover, the house once belonged to a sage, which gives Yuuya access to remarkable weapons, equipment, and crops with extraordinary effects. With these newfound blessings, the once-undesirable Yuuya may just reach his true potential and become unstoppable.

On her way to school one day, Suzume Iwato stumbles upon Souta Munakata, a young man searching for abandoned areas. The high school girl directs Souta to a nearby ruin, but out of pure curiosity, she herself decides to head to the same destination. Once there, Suzume discovers an isolated door with a dreamlike universe lying beyond it—a place that she can see and feel, but not enter. A strange stone rests on the ground nearby, but it turns into a cat-like creature and scurries away when Suzume lifts it. Suddenly afraid, she heads back toward her school, not realizing that her act of leaving the door open will have consequences. With the keystone released, the evil within the other universe can now freely escape and wreak havoc throughout Japan. Intending to correct her dangerous mistake, Suzume joins Souta—whose true goal is to prevent evil from festering—in finding and locking all open doors before the country is destroyed.