An oldie from the vaults.

Alicorns, anthropomorphized unicorns, live with their wretched enemies, dragons. And for some pure alicorns, the wretchedness consumes them, cursing them to change into their hated adversaries. For Sarwal, the possibility he, too, may be infected with the curse makes him seek out solitude, for fear of harming those he may love.

From 2006, no updated editing. Story only.

Available as a 3-ticket download now on the store: http://tfx.mangaweb.net/