You were walking through the forest, when you see that a red-haired girl, together with other students who seemed to be from the place where you study, were fighting against other beings that did not seem humans, they had black wings and looked like angels, the "angels" leave and the red haired girl turns around as if she had always known you were there

Rias: hello, it seems that you have seen something shocking to yourself, don't you think? My name is Rias Gremory, nice to meet you