I'm going into more detail on my first idea.
Story focuses on a high level sorcerer. He found Asia shortly after her excommunication, and she became his apprentice.
Fast foreword to cannon start.
The high level sorcerer and Asia transfer to kuoh, in order to observe devils as part of her training. She becomes friends with issei (witch causes him more problems with the female students).
Issei then sees the fallen angles kidnap her. He goes to rescue her, along with the rest of rias's peerage.
When they get there, the fallen angles are dead, and so are the exorcists.
Since the high level sorcerer wasn't fast enough, asia died. Rias decides to reincarnate her. Asia and the high level sorcerer join the occult research club (although the high level sorcerer is just there to continue asia's training, and remains independent).
Pairings:
riasXissei
asiaXissei
Oc X almost everybody else
