Apparently, the outfits are ALL for the new single..
Perhaps they want to show the sides of Japan / Asia..
So they use kimonos, office lady, schoolgirl, and "professional" outfits.. and I don't know about Aika.
Reina + Koharu -> school
Eri + Miki -> office lady
Yossie + Risa -> professionals
Ai + Sayu -> kimono~