Legendary Sword?, O_o Options

[Guest_Zio_*]

I actually found this out when I was helping out my friend when playing offline and if you go behind the house that you stay in there is a tree with a sword next to it and its stuck in the ground. You can attempt to pull out the sword but I havn't been able to pull it out. Maybe you can pull it when you complete all the offline or online quests or both? Also I don't think the game talks about it at all so was just kinda wondering what it is.