The Arrival! Doppelganger, am I Nagisa?

I'll Make a Habit of It – Season 1

Nakatake meets Kozue, who he thinks IS Nagisa for a moment. Later, Nagisa collapses on set, needing time to recover. Nakatake gets Kozue to fill in while Nagisa recovers, but during that time, Kozue falls in love with being a Super Idol.