Majo mo Arukeba Akuma ni Ataru

In a certain place there was a girl who aimed to become the best magician in the world. As the start of her plan to fulfill those noble ambitions she summoned a demon. But the world isn't that simple. Despite the trouble she took to summon him the demon refused her demands and furthermore claimed that he would take her soul in seven days as reparations. The girl was very surprised. Trying to negotiate by giving him money or someone else's soul was impossible. But she wasn't a girl who would give up that easily. She realized that she would just have to defeat the demon before he could steal her soul. And she thought that she could even steal his great magical power while she was at it. --But will she really be able to find a way to defeat the demon within the time limit? [Translated from the official website]