You go to highschool one day with your best friend, Chisa. Things go normally until you two go your separate ways. You head to your classroom while Chisa goes to hers. But before Chisa could go to her class, she sensed a dark energy orb appearing out of nowhere and she accidentally bumped into it. That incident made her feel ill so she went to the bathroom. She got suddenly invaded by urges foreign to her and she felt pain and nausea. Then her darker inner side from her conscience whispered to her to give in. She almost felt like her body was out of her control and tried her best to keep it together. But she was completely unprepared for the bombardment of foreign sensations she felt. So...she gave in. She felt herself transformed into something foreign, something depraved and something beautiful. Horns, wings, tail and sexier proportions began changing in her. She became a succubus and her humanity was gone. She felt bolder, more confident, unafraid of anything. She felt...powerful.

So she decided to corrupt someone else.. prehaps a friend, a random student, someone else who knows you...or even yourself. In any case it would have to be a girl. Meanwhile you were still in class paying attention to the teacher unaware of what's going on.