After 1/2 hour searching an answer to my question on the forums, I've decided to create a topic about it, since I have my own theory B-)
So, we know that the 5 kidnapped girls (Ruka, Misaki, Madoka, Marie, Tomoe) performed the Kiraigou, and I assume that they were each assigned a role (singing, flute, drums, chimes and strings) right? Well my question is, do we know who had X role ?
And if not, do you have your own theory about it? Or maybe I'm wrong and no instruments were used in the Kiraigou ?
On the BCL wikia, I saw on the Spirit List that the five Kanade who performed the Kagura (with Tsubaki) each had had a different fate (for instance, about the 'Song' Kanade, her 'voice became dry and raspy', see more here) , so I tried to link these Kanades' fates with the 5 kidnapped girls'. Okay so it's a little far-fetched but here's my theory;
-Ruka was the 'Chimes' Kanade, as the other one who 'lost her memory and left the island'.
-Misaki was the 'Sing' one, as the other one whose 'voice became dry and raspy' -> could be metaphor to say Misaki became "curt" (see how she talks to Madoka in the Opening Cutscene?)
-Madoka was the 'Flute' Kanade, as the other one who was 'unable to laugh after the Kagura' -> it fits, because Madoka appears as an anxious and frightened girl, scared that Misaki would remember Miya
- Marie & Tomoe were the 'Drums' and 'Strings' Kanade, as the other ones ultimately went missing and/or died -> in the beginning of the game, they're already dead, so it fits!
Here is my two cents theory haha, if you have an answer to my question or your own theory, well... your turn B-)