The Soulaxe is one of the possible three unique weapons crafted by Orthanc in SpellForce: The Order of Dawn.

I could make you a weapon you've never even dared to dream of, warrior. But for that I need material that is more precious than a kingdom.
Orthanc about his plans

Upon having completed the quest Soulstones it will be handed over to the Phoenix Bearer. It was made for heavy fighters to deal great damage but its heavy weight, makes it rather slow.

The other two soul weapons