the answer... I could not find... no matter how hard I tried

Lorelei

Lorelei, a beautiful young maiden, committed suicide because of an unfaithful lover. She jumped from the steep rock into the Rhine River, thus killing herself. She then became a siren, luring shipmen to their fates with her hypnotizing voice. The echoing heard today is said to be Lorelei.
- excerpt from Wiki

In my opinion, the name is odd, considering that the weapon's element is fire as opposed to water, and its master is not a man of many emotions or words that would lure anyone anywhere. Ein's Diviner is Einherjar - alluding to the souls taken to Valhalla to fight in the Ragnarok. Ein 'recruits' the sprites of Riviera to prepare for the battle to save their world. That one is kind of straight forward.

We'll assume that it is referring to the fact that Ledah is one of the strongest Grim Angels, making him a deadly and formidable opponent who lures his opponents to death. That was a bit of a long haul there, but it sort of works, right?