Alicorns want their kind to survive.

The Goddess and Red Eye promised them procreation by magic. Now, they are both dead.

Velvet Remedy says that they need zebra shamans, but this is still uncertain.

But a lone purple Sister, cut off from her fellow alicorns in some area of the Equestrian Wasteland systematized all her knowledge about this vital topic and chose third path. A path, that requires an experiment with two participants. So she goes on the hunt.

Unfortunate (or vice versa, depends on point of view) earth pony stallion became her first prey...

01.09.2016: Wr3nch kindly agreed to proofread and edit this story. I can't thank him enough for this.
He also edited Fallout Equestria: Sisters, so if you like not-exactly-pony protaginists, and/or alicorns you may also give it a shot!