One day, she helps an old homeless woman, who in turn, gives her a necklace. The necklace has the power to summon 4 other girls, from other worlds and dimensions, when Yonaka needs them. Each of these girls have their own powers, and abilities to help Yonaka with certain things.
Then, an evil force descends(you were expecting otherwise?), looking for the necklace, because they want the girls to help them destroy the universe. And whoever holds the necklace, the 6 girls are under their command. The old woman appears again, this time in her true form, and grants each girl even more powers over a certain element(hence the name, GENSO, which means element), and the ability to change into a creature of that element, fictional and real.
This is the story of the GENSO 5, and their quest to save the universe from annihilation(hmmmmmmm, I think this sounds like a commercial for promoting the manga. " Buy GENSO 5, and YOU can save the universe from annihilation too!*toothpaste grin*". Don't you think it sounds like a commercial?).