Goro Amamiya, a small-town obstetrician, has his world turned upside down when his favorite pop idol, Ai Hoshino of the group B-Komachi, appears at his clinic. She is pregnant with twins and desperate to keep the birth a secret to protect her career. Goro vows to support her, but on the night she goes into labor, he is murdered by an obsessed fan. In a strange twist of fate, Goro reincarnates as one of Ai's newborn sons, Aqua. He soon learns that his twin sister, Ruby, is also a reincarnation, a former patient of his who idolized Ai just as much as he did.

The twins watch their mother rise to unprecedented fame while hiding her motherhood, but their happiness is shattered four years later. On the morning of a major concert, a stalker breaks into their home and fatally stabs Ai in front of her children. As she dies, Ai whispers a cryptic declaration of love, leaving Aqua and Ruby with more questions than answers. The live-action series follows the twins as they grow up and enter the entertainment industry. Ruby pursues her dream of becoming an idol like her mother, joining a revived B-Komachi. Meanwhile, Aqua becomes an actor, driven by a secret obsession: to identify and take revenge on the man responsible for Ai's murder, who he believes is his biological father.

The eight-episode drama charts their journey through the dark underbelly of show business, from reality dating shows to grueling stage productions, as they navigate lies, rivalries, and the heavy legacy left by their mother. The story concludes with the feature film Oshi no Ko -The Final Act-, which adapts the final arc of the original story. As the truth behind Ai's past is uncovered, Aqua and Ruby are forced to confront the devastating reality of their origins. Aqua’s quest for vengeance reaches its peak, putting him on a direct and dangerous collision course with his father, Hikaru Kamiki, a shadowy figure whose manipulative cruelty has left a trail of destruction through the entertainment world. The film brings the twins' intertwined fates to a final, dramatic resolution, revealing the full meaning of Ai's last words and the true cost of the lies that built their family.