User blog comment:Lasifer/Hellstorm Issue 6: Beowulf vs. Achilles/@comment-4661256-20130619215941/@comment-422690-20130624221607

The former was never mentioned, so it would he the latter. It's described as incredibly dense, heavy, and massive, so I'd say it's that he's the only one strong enough to fight with it. Beowulf could break it, but I think he'd find it harder than you're saying.