The are some ideas about Haruka the new idol:
-Haruka will meet STARISH and QUARTET NIGHT when haruka was practising her singing that she just make.
-They suddenly felt somehow that the song reminded them about Haruka made it when she was their composer.
-Kou was surprised to see STARISH and QUARTER NIGHT outside of Haruka practice room when he also heard of Haruka singing too.
-When Haruka was done singing she was shocked to see them outside staring at her with amazed,shocked and confused faze,the all thought in wonder was this this girl familiar to haruka to they all know.
So this is like my ideas about the story,I'm not sure this good or not but please recommend. And so I hope you can update this story Author-san