Shuuichi Kagaya is what one would consider an average high school student, but sometimes, he turns into a monster. He doesn't know how or why he got his abilities, only that he would prefer no one knows about them. One night, he finds a building ablaze with a girl trapped inside. Deciding to save her, he transforms and carries her to safety, but accidentally drops his phone. The next day, the girl he saved—Claire Aoki—finds him and confronts him about his monster identity. She even goes so far as to push him off the school roof to prove her theory after Shuuichi denies her allegations. Desperate to save himself, he transforms, and Claire snaps a picture in order to blackmail him into telling her everything he knows about monsters, which, ironically, isn't much. As it turns out, Claire has a secret of her own: she has been searching for her sister, who also became a monster. She enlists Shuuichi's help to track her down, but they aren't the only ones searching for answers.

One night, as meteors streak across the star-studded sky, Shion Pavlichenko becomes a Contractor. Despite her brother's transformation, Shion's twin sister Suou continues to live a fairly ordinary life, attending middle school with her friends and getting caught up in the awkwardness of growing up. However, everything changes when her home is invaded by a masked man cloaked in black, destroying any sense of normality she once had. Revealed to possess latent Contractor abilities of her own, Suou is caught between family, friends, and her own sense of purpose as she ventures into the ruthless world of cutthroats and espionage that Contractors call home. Meanwhile in Tokyo, investigation surrounding Hell's Gate's sudden collapse is underway, and prophetic signs of doom point in the direction of a silver-haired doll.

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.

Equipped with his passion for diving and admiration for marine biology, university student Tsuneo Suzukawa tries his best to juggle several part-time jobs to earn enough money to study abroad. But one night, in a fateful accident, he meets a girl in a wheelchair, driving his current path into a detour. The girl, Kumiko—who prefers to be called Josee—initially comes off as rude. Tsuneo, however, is then convinced by Josee's grandmother to take on the paid job to be Josee's caretaker. Despite being annoyed with her bossy demeanor, Tsuneo sees the opportunity to save more funds to support his academic dream. Nonetheless, after putting up with Josee's behavior for some time, Tsuneo tries to quit, only to discover Josee's dreams of traversing the outside world—to experience a life free from her crippling condition. Changing his mind, Tsuneo decides to accompany Josee in exploring the wonders that the world has to offer. Through their time together, the two begin to realize that the traits that bind them may be vital toward fulfilling their respective aspirations.