Key of Lorelei

A mighty weapon created by Lorelei which allows the user to summon Lorelei when used along with the Grand Fonic Hymn. It also allows the user to use Lorelei's power at will. The complete Key is actually in two parts: A sword, (also called the "Key" of Lorelei) which concentrates Fonons, and the Jewel of Lorelei, which disperses them. Both halves of the Key are almost useless unless combined.

The Key of Lorelei was given to Yulia as part of the pact. It was used in order to create the Planet Storm, and possibly, the other Sephiroth as well. During his imprisonment by Van Grants, Lorelei sent both parts of the Key to Luke and Asch. Asch received the sword itself while Luke was to be given the Jewel. Luke however, did not receive anything to his knowledge, and both Asch and the party desperately search for it. However, on the Tower of Rem, it is discovered that Luke received the Jewel as he was meant to. It just so happened that Luke accidentally absorbed the Jewel into his body, as both the Jewel and himself (being a replica) are made of Seventh Fonons.

After defeating Asch on Eldrant, Luke wins the sword, which combines with the Jewel to form the "Incomplete Key of Lorelei". Later, after Luke gains the power of second-order hyperresonance, that ability allows him to fully complete the entire Key. He uses the Key and his own power in order to defeat Van and free Lorelei.