Starlight Blue ~Osananajimi de Oshi no Ko ga Shiranai Uchi ni Kaihatsu Sareteita~

Asuka Rin is diligently working toward her dream of debuting as an idol.
The protagonist, Toki Yuzuru, supports her from close by, quietly watching over her efforts.
Though the two are childhood friends who share special feelings for each other, they’ve chosen not to become a couple, prioritizing Rin’s aspirations instead.

Izumi Touya, the president of the production company Rin belongs to, tries to take advantage of her by dangling the promise of a debut. However, things haven't gone as he hoped.

One day, Yuzuru—who works part-time at the company—loses a USB stick containing important data he was entrusted with.
Held responsible, he finds himself in a difficult situation.
To protect Yuzuru, Rin resolves to accept Touya’s offer of a “special private one-on-one lesson” in exchange for her idol debut.

Until a few days ago, another trainee had been living with Touya in his home, but she has since left.
Now, Rin and Touya are alone together.
Despite her unease about the private lessons, Rin steels herself—for Yuzuru’s sake.

From that day forward, Yuzuru begins to notice Rin gradually changing... and can't shake the feeling that something is terribly wrong——.