Aeris/Sephiroth is actually quite popular. One of the first ever fanfics I read was about that pairing.

It works quite well if you get a pre-Nibelheim Sephiroth with her.

Or, in one of the fanfics I've long since wanted to write but which I'm certain would be awful because I lack the technical ability to do it justice, where Sephiroth succeeds in killing Cloud and leaves the reactor. He would still be distraught with confusion and thinking he was an Ancient. He'd go to the Shinra HQ, find the records on the last known living Ancient, and go find Aeris. I haven't thought of how they'd get together exactly but that's the premise.

The point is you need the tragic interpretation of Sephiroth and not the bland evil one that is seen in the present time of the game.