Kana thought Aqua would confess to her Oihi no ka ep5

Gynecologist Gorou Amemiya is tasked with helping deliver the children of Ai Hoshino, a Japanese idol whom he admires, without the knowledge of the general public. However, the night of Ai's delivery, Gorou is murdered by an obsessive fan of Ai's, and is reincarnated as Aquamarine "Aqua" Hoshino, Ai's son, retaining his memories of his previous life. Aqua's fraternal twin, Ruby Hoshino, is also a reincarnation, though she refuses to admit her original identity as one of Gorou's patients who got him interested in Ai in the first place. Four years later, Ai is murdered by the same obsessive fan, who later commits suicide. However, Aqua pieces together that the fan must have had his and Ruby's father as an accomplice and thus resolves to enter the acting world to find and kill his father.

Twelve years later, Aqua joins various productions to get DNA samples to test against his own. He eventually meets his half-brother, Uehara Taiki, during a stage production, who tells Aqua that Taiki's parents committed a double suicide, but Aqua learns that their suicide happened before Ai's murder. Aqua's girlfriend, Akane Kurokawa, finds that the twins' actual father—Hikaru Kamiki—is alive, but Aqua cuts ties in an effort to protect her. Meanwhile, Ruby starts an idol group under the same name as Ai's original group, joined by aspiring actress Kana Arima and Youtuber Mem-Cho. On an out-of-town MV shooting, Ruby finds Gorou's corpse and runs into a mysterious child who confirms that her father was responsible for both Gorou and Ai's murders. Fueled by revenge, Ruby throws herself into her idol career, propelling both her solo and idol group's careers, though it ostracizes her from Aqua, Kana, and Mem-Cho. Desperate to prove herself, Kana successfully establishes inroads with a famous director, but a tabloid captures her following the director back to his apartment and prepares to write an article suggesting that she is his mistress. To prevent this, Aqua leaks his and Ruby's identity as Ai's children, fracturing the twins' relationship.