Song of Nephilim as it appears in Episode I.
The Song of Nephilim was a pyramid-shaped space station that was one of the major causes of the Miltian Conflict. When activated, it generated a wavelength that was not truly audio in nature, but psychic. Only a very few special people, usually powerful psychics, are capable of hearing the "song," which is perceived by them to be the haunting singing of a female voice. However, it does not need to be heard to affect those within its range. Realians are most affected; however, even humans can fall into madness upon prolonged exposure to it. The song is thought to summon Gnosis, but their appearance is actually a side-effect due to the barrier between real and imaginary number space weakening due to U-DO's increased scrutiny over those affected by the song. The Song causes fragmentary contact with U-DO due to its use of an unstable recreation of Lemegeton, and was used by Joachim Mizrahi to sever Old Miltia's continuity with the UMN (through overloading it). It was used during the Miltian Conflict as well as the Kukai Foundation incident in Episode I; Gnosis swarmed the space between Kukai and Second Miltia. Albedo used the Song and its power to lure MOMO and, ultimately, Rubedo to him. Furthermore, the Song of Nephilim was a key component of Proto Merkabah (the Song was the power source for Merkabah; therefore, when the two space stations merged, a superweapon was created), as well as another Joachim Mizrahi invention. However, the Song is apparently destroyed, for it was docked with Proto Merkabah during the latter's destruction.
According to the web digest "Missing Year" (available at the official Japanese Xeno website, translations available at Labyrinthos.org), Joachim Mizrahi developed the Song of Nephilim system based on the work of another scientist during the Lost Jerusalem era. A man named Grimoire Verum was researching the newly-discovered Zohar and its connection with the Gnosis. He developed a "program" (what is meant by program is unknown) called "Lemegeton" that influenced the behavior of the Gnosis, but his experiments failed, resulting in the local matter shift (space-time anomaly) that caused the disappearance of Earth. Mizrahi dubbed the system the "Song of Nephilim" because "Nephilim" was one of the only recognizable words Mizrahi discovered with the wavelength.