The Phoenix: Rettenjo (
After discovering Kushinada's Lynchpin, Nine had it taken to her laboratory underneath the Magister's City of Ishana. There, she removed its core and created the Phoenix: Rettenjo, a large nail which was to be used to destroy the other Nox Nyctores after the end of the Dark War. It was not designed to combat the Black Beast, but was outfitted with a core made from a fragment of Gigant: Take-Mikazuchi's.
Nine feared that she would not live beyond the Dark War, so gifted it to Trinity Glassfille, her best friend and the wielder of the Arma Reboare: Muchourin. It was stored in a box and kept hidden by Trinity. Nine made clear that Rettenjo was to be used to destroy the Nox Nyctores because of their power. Countries could destroy others with ease, or a Nox wielder made insane could prove too destructive. After the war ended, Nine removed Rettenjo's core, but its whereabouts became unknown after Nine was killed by Terumi.
Nearly 80 years after the war had ended, Rettenjo had found itself in the possession of Tenjo Amanohokosaka. She refused to use it in conjunction with the Kushinada's Lynchpin during the Ikaruga Civil War and sealed her soul within it before giving it to Bang Shishigami to protect it.  Bang was never told the details of the weapon, but eventually nailed it into the Lynchpin, sealing off the seithr from the world. It remained within the Lynchpin in the world created by the Embryo while another version of it was in Bang's possession. Ragna the Bloodedge took the wish of Tenjo while her soul slept within the Rettenjo. It is presumed in the new world created by Ragna that the Rettenjo still rests within the Lynchpin, as it was not seen on Bang's back in the finale of BlazBlue: Central Fiction. 
The Nox takes the form of a 55-inch nail with a wide circumference. Underneath its head is tied a bright red scarf. Rettenjo has the properties of being able to stop the flow of seithr and destroy the other Nox's that exist.  Other than its physical abilities as a melee weapon, it has little to offer in the way of combat.
BlazBlue: Central Fiction Library Entry
Nox Nyctores number 9. Possessed by Bang.
It was once possessed by Tenjo. It's also known as the 55-inch nail. It was developed by one of the Six Heroes, Nine, as the core of 'Kushinada's Lynchpin', and an 'Anti-Nox Nyctores' weapon. It has the power to destroy other Nox Nyctores. 
A Phoenix is a mythical Greek bird that rebirths itself after each death by resurrecting out of its ashes.
The Japanese can roughly be translated to "Phoenix Wing: Splitting the Heavens Above." The character used for phoenix can also refer to the Chinese phoenix, which is associated with the position of empress.
- BlazBlue: Phase Shift 4, Chapter 3 – Demonic Human Weapon
- BlazBlue: Phase Shift 4, Chapter 5 – Blue Snake's Crazed Play
- BlazBlue: Spiral Shift - Hero of the Frozen Blade, Chapter 4
- BlazBlue: Central Fiction, Story Mode, Episode 012, Chapter 100
- BlazBlue: Chrono Phantasma, Arcade Mode, Bang Shishigami - KUSHINADA
- BlazBlue: Central Fiction, Library Mode, Weapon #009