Adult life has brought its share of disillusions to 28-year-old writer Sumireko Ogawa, who was once considered a child prodigy in literature. Facing hostility from editors, she struggles to publish her work and progress in writing her new novel. As Sumireko starts to resign herself to the uneventful life of a book clerk, she is brutally plunged into the realm of mysteries after she reads poetry from a strange book, as she unexpectedly becomes a child again. Sumireko is thrilled to have regained her inspiration and youthful enthusiasm. However, her work colleague Ren Adashino, who happens to be an expert in the occult, warns her that this transformation will eventually kill her unless she reads other verses from the book. Reluctantly agreeing to regain her adult form, Sumireko decides to help Ren and his sister, Oto, in their paranormal investigations. Although Ren's goals are still unclear to Sumireko, the young woman is determined to turn her new exciting life experiences into a lasting literary success.

Mahiru Kouzuki, a skilled artist, gives up on her passion after her elementary school classmates ridicule her colorful jellyfish mural. Several years later, upon encountering an unexpected admirer in Kano Yamanouchi—a former idol with a troubled past—Mahiru decides to pursue her childhood dreams once more. Tasked with designing the mascot for Kano's new music project, JELEE, Mahiru enlists the help of her childhood friend and professional streamer Kiui Watase to make JELEE's first music video. Together with Kim Anouk Mei Takanashi, a pianist and fan of Kano's work as an idol, the girls aim to turn JELEE into a global hit. However, if they want to succeed in this ambitious endeavor, they will first have to free themselves from the shackles of their pasts.

Shintarou Tokumitsu leads an ordinary high school life while living in a studio apartment just for himself. This changes drastically one morning after he finds something strange on his balcony—an angel from Heaven. The innocent and kind girl named Towa was sent to Earth by God to learn more about humans and their way of interacting. It does not take long for her to get attached to Shintarou, who eventually allows her to live with him. However, the small apartment provides little personal space and privacy, and hiding Towa's real identity from the public proves difficult. As he learns to navigate his new life with Towa, Shintarou's encounters with other girls may only complicate the circumstances.

Hikaru Amatsuga's days of tranquility come to a sudden end when he rescues Alma, a mechanical arm crying for help. Alma fuses with his jacket, introducing Hikaru to the world of mechanical arms: mysterious, sentient weapons that normally become a part of their users' bodies. Forced to flee for his life, Hikaru is eventually captured by Aki Murasame, a twin mechanical arms user working for ARMS, an organization that protects the machines against unethical treatment. The Kagami Group, a nefarious organization that treats mechanical arms as mere tools, seeks to recover Alma. Hikaru is deemed a failure by ARMS for his lack of natural predisposition to be an mechanical arm wielder, so Aki is assigned to be his bodyguard. But Aki is defeated by Jun Kagami, who cruelly tears out her two mechanical limbs, condemning the girl to a slow death. Unwilling to abandon Aki to her grim fate, Hikaru miraculously awakens his power and neutralizes Kagami. Now a full member of ARMS, Hikaru is determined to unravel the truth about mechanical arms and protect his newfound friends and allies.