Rainbow Heart was the name of the magical country's army. Because of that, everyone in it was a magic user. The centerpiece of that army were seven magical girls, the strongest magic users that had been given the rainbow title. Rainbow Heart worked for peace and the proper use of magic. Simply put, they would fight demons or capture people who used magic for selfish reasons.
Rainbow Nana, former.
Yurika Nijino, Successor of Rainbow Nana