Ririchiyo Shirakiin is the sheltered daughter of a renowned family. With her petite build and wealthy status, Ririchiyo has been a protected and dependent girl her entire life, but now she has decided to change all that. However, there is just one problem—the young girl has a sharp tongue she can't control, and terrible communication skills. With some help from a childhood friend, Ririchiyo takes up residence in Maison de Ayakashi, a secluded high-security apartment complex that, as the unsociable 15-year-old soon discovers, is home to a host of bizarre individuals. Furthermore, their quirky personalities are not the strangest things about them: each inhabitant of the Maison de Ayakashi, including Ririchiyo, is actually half-human, half-youkai. But Ririchiyo's troubles have only just begun. As a requirement of staying in her new home, she must be accompanied by a Secret Service agent. Ririchiyo's new partner, Soushi Miketsukami, is handsome, quiet... but ridiculously clingy and creepily submissive. With Soushi, her new supernatural neighbors, and the beginning of high school, Ririchiyo definitely seems to have a difficult path ahead of her.

Since the death of his parents, Shinpei Ajiro had lived with the Kofune family and their two daughters—Mio and Ushio. Although he then left his home island to continue his education in Tokyo, Shinpei returns after Ushio tragically drowns during the attempted rescue of a little girl. During the funeral, his best friend informs him about bruises found around Ushio's neck, casting doubt over the cause of her death. Suspecting a murder has taken place, Shinpei reevaluates recent events, but strange incidents only continue to transpire. Disappearing people and other unexplainable occurrences lead Mio to recall an old folktale referring to entities called Shadows, which may not be entirely fantasy. Supposedly, an encounter with one's Shadow foretells the person's impending demise. Facing the dark side of Hitogashima Island, Shinpei stands against his grim fate to fulfill Ushio's final will—to protect Mio.

On one noteworthy day in the Adventurer's Guild, Kazuma Satou encounters someone unexpected—a fan of his named Ran. Surprised that he even has a fan, Kazuma attempts to play it cool to impress her. Unfortunately for him, the guild's receptionist arrives with a request to defeat a giant golem guarding some ancient ruins, and Kazuma accepts only to keep Ran's admiration. Upon Kazuma and his party's successful return from the ruins, Kazuma continues to shamelessly brag to Ran. Capitalizing on his desperation, the receptionist approaches him with another quest that requires him to return to the same ruins. Hoping to find valuable treasures, Kazuma once again convinces his party to join him—but this time, he may be biting off more than he can chew.

Two souls, living very different lives, wander alone and isolated in their respective worlds. For nine-year-old Ren, the last person who treated him with any form of kindness has been killed, and he is shunned by what is left of his family. With no parents, no real family, and no place to go, Ren escapes into the confusing streets and alleyways of Shibuya. Through the twists and turns of the alleys, Ren stumbles into the intimidating Kumatetsu, who leads him to the beast realm of Shibuten. For Kumatetsu, the boy represents a chance for him to become a candidate to replace the lord of the realm once he retires. While nearly unmatched in combat, Kumatetsu's chilly persona leaves him with no disciples to teach and no way to prove he is worthy of becoming the lord's successor. While the two share different goals, they agree to help each other in order to reach them. Kumatetsu searches for recognition; Ren, now known as Kyuuta, searches for the home he never had. As the years pass by, it starts to become apparent that the two are helping each other in more ways than they had originally thought. Perhaps there has always been less of a difference between them, a boy and a beast, than either of the two ever realized.