Where is Cooley?

(from ebookjapan):
Yoko Kuriuki, aka Cooley, a popular singer, was good enough to win a rookie of the year award, but suddenly disappeared from the entertainment world. One day, Cooley's cousin Yumiko happens to see Ogita, who used to be Cooley's backup guitarist, on the street and follows him. She follows him and succeeds in forcing him to meet Cooley... but Cooley can only speak in private and cannot sing anymore.... However, her manager Karashima thinks that Yumiko, who has a similar face and body shape to Cooley, might be able to take Cooley's place when he hears her sing, so he takes a chance on her...?

Note: The second volume contains the two one-shots from the "Reject Series", a short-lived series of one-shots Takeda did for Monthly Seventeen (Gekkan Seventeen) in 1979 that stopped abruptly after the second one-shot. These are absent from the digital edition.