Faer'tali Eru (3.5e Equipment)
From D&D Wiki
This +6 adamantine flaming burst keen bastard sword bears a strange, almost organic looking blade that bears a flowing line of spiraling runes along its length. Clearly not made to be use by a human hand, the hilt wraps around its wielder's hand, seeming to become a part of it.
In addition to it's normal abilities, when used to deliver a hideous blow invocation, the wielder's eldritch blast ability deals an additional +10d6 points of damage.