The Different Dimension Destruction Device (異次元壊滅兵器 Ijigen Kaimetsu Heiki), D4 (ディーフォー Dī Fō), is a superweapon developed by GAFJ, first appearing in the Ultraman Z episode of the same name, D4. The prototype D4 took the form of a stationary explosive. Following the success of the prototype during its detonation test, two production units were constructed, this time taking the form of an energy projectile based on the technology of the prototype, and designated as the D4 Ray (
Following Baraba's destruction at the hands of Ultraman Z and Ultraman Ace, the Terrible-Monster's sword was left behind. Upon studying the sword, Yuka Ohta excitedly revealed that the sword had the ability to breach the boundaries between dimensions and open pathways to new ones. It can be assumed that the development of D4 began shortly after this.
From said sword, GAF was able to study the energy matter of Yapool's Alternate Dimension portals. After construction of a working D4 device was completed, the weapon was tested in an uninhibited island a significant distance off the coast of Japan, Nakanotorishima. The resulting test was successful, and created a massive crater on the island, prompting GAF to request Kuriyama have the weapon fitted onto King Joe STORAGE Custom's Pedanium Particle Cannon, much to STORAGE's dismay. A second D4 was constructed, this time an energy projectile version referred to as the D4 Ray, and loaded into King Joe's collection of weaponry.
Right from the start, it became clear that the first D4 had created serious problems, as the energy released drew the attention of a Kelbim, who had been sent to Earth by the Mother Kelbim to begin an invasion that would allow the species to infest the planet in search of energy, then propagate the species further. After landing on Nakanotori Island, Kelbim made his way towards the STORAGE HQ in Japan, intent on obtaining the energy in the D4 Ray. Along the way, Mother Kelbim began launching more Kelbims in their meteorite forms at Earth, eventually amassing a small army of the creatures on Earth via the Kelbim amplifying the Mother's signal to activate more of the meteorite forms.
As GAF was intent on having the D4 Ray be used in the battle, Kuriyama repeatedly attempted to make Hebikura give the order to fire the D4 Ray, but he refused, and Yoko attempted to fight for as long as possible without having to use it.
Eventually, the weapon was fired, destroying the Kelbims, but then triggering a near-collapse of Earth's dimension, causing the entirely vacant city of Tokyo to be consumed by the excess energy as it tore apart the fabric of reality itself. Ultraman Z Delta Rise Claw managed to stop its spread with a boosted Zestium Beam. However, a large area of the city was left devastated.
Despite the devastation the D4 Ray had wrought, GAF continued its research into utilizing the weapon, and developed a purpose-built Special Airborne Armor unit, Ultroid Zero, to use it, with a second D4 Ray unit mounted inside. GAF Strategic Manager Mai Yuki and her team of scientists had come to the conclusion that the secret to controlling the D4 Ray's energy lay in how Ultras used their beams, and needed data on Ultraman Z's abilities to be able to use the D4 Ray safely. During Ultraman Z, Sevenger and King Joe STORAGE Custom's battle against Alien Barossa III and Tri-King, this data was gathered when Tri-King used King Joe STORAGE Custom as a meat shield against Z's Zestium Beam.
Ultroid Zero's new D4 Ray first saw use against an onslaught of monsters, though the recoil it produced knocked Yoko out. Celebro managed to possess Yoko and use her to take control of the machine as part of his Civilisation Self-Destruction Game, with his intention to steal the D4 and use it to destroy humankind and ravage the Earth being his goal all along.After being recovered by GAF, Ultroid Zero underwent further modifications and repair work to seemingly eliminate this further setback, but
After absorbing the energy of the Kaiju Medals and the energy and genetic material of a set of seven monsters across the planet, Ultroid Zero transformed into the chimeric monster Destrudos, with the D4 Ray being incorporated into Destrudos's body. This version of the D4 Ray, known as the Destrudo D4 Ray (デストルド
The Destrudo D4 Ray was destroyed along with the rest of Destrudos's body at the conclusion of the final battle between Z and Celebro.