Yumekoi ~Yume Miru Mahou Shoujo to Koi no Jumon~

Akira takes care of his younger sister Kurumi while their mother is away on business. One day a girl named Kurumi arrives and claims to be a magical girl from the magical world parallel to our own. She's the alternate reality version of his own sister Kurumi. Kurara, Kurumi's guardian mascot character arrives and explains to Akira that Kurumi has actually run away from home and she must bring her back! To make matters worse three Dream Flowers have followed her to our world. They have the power to make ordinary girls into magical girls and they must retrieve them at all cost. It's too late however because the missing Dream Flowers have already entered Akira's sister Kurumi and two of their friends, Sakuya and Mei and because our world is a world of science the magical power in them is out of control, they cause the girls to have overwhelming sexual desires. Now they must use their magic to make the flowers bloom in order to graduate from being magical girls and return the Dream Flowers to the magical world.