User blog comment:MeritC/Calling all Aikatsu/Aikatsu Stars Wiki members who also have a GameFAQs account!/@comment-26426093-20160529132035/@comment-3487190-20160529143044

I don't think we can have comfirmation about the "main girl" thing cause there's no official definition about this.

1) Remember the old series, they kept adding new girls and only until the unit group story when they begin to focus on only one unit. However we don't know how would the rookies do units in the future.

2) In the Stars series, the other important thing is the new singers. Only Rie and Sena the new entries sing for the icon songs, probably cause it's BANDAI and Lantis' strategy. We haven't known if Koharu, Ako and Mahiru have their singers perform in the future.

Just in a view of story, so far only Yume and Rola have main stage scenes, and Koharu has extra story role. Although Ako and Mahiru had made appearance, they haven't officially become part of Yume's gang.