From Bulbapedia, the community-driven Pokémon encyclopedia.
The ultimate weapon (Japanese: 最終兵器 ultimate weapon) is a weapon created by AZ 3,000 years prior to the events of Pokémon X and Y, located in Geosenge Town. It features heavily in those games, and is referenced in Pokémon Omega Ruby and Alpha Sapphire as well.
The weapon has a similar shape to a flower, and it appears to be made of a crystalline material. The machine was powered by the life force of Pokémon, whose graves line Route 10. This energy source was later used by the Devon Corporation and named Infinity Energy.
Pokémon X and Y
Originally, the machine could only bring Pokémon back to life, and was used in that capacity to revive AZ's Floette. Exposed to the power of this machine, AZ gained immortality. AZ still wanted revenge on those who had killed his beloved Pokémon, and converted the device into a weapon that he used to end the great war by destroying both sides. When AZ's Floette realized that so many lives were lost merely to restore her own, she left AZ. The weapon was later buried deep underground by AZ's brother to try to prevent it from being used again.
In the present day, Lysandre, the boss of Team Flare, aims to use the ultimate weapon to destroy all life—including Pokémon—to create a more beautiful world. However, it could only be reactivated with the power of the Kalos Power Plant, XerneasX/YveltalY, and the key possessed by AZ.
To accomplish this lofty goal, Team Flare occupies the Kalos Power Plant and diverts enough electricity to the weapon to cause a blackout in Lumiose City. This electricity is used along with the power of the Legendary Pokémon to reactivate the weapon, allowing it to surface once again. However, when the player catches XerneasX/YveltalY, it drains most of the energy from the weapon. Lysandre then attempts to use what little power still remains to make the player and their friends immortalX/destroy Team Flare Secret HQ and everyone insideY, but the beam it launches falls back on itself, and buries the HQ and Lysandre under the rubble, leaving a crater in the center of Geosenge Town.
According to Professor Sycamore, Mega Stones are special stones such as Evolution stones that were irradiated by the power of Xerneas and Yveltal that was fired from the ultimate weapon.
Pokémon Ultra Sun and Ultra Moon
In Pokémon Ultra Sun and Ultra Moon, Lysandre claims to have passed out after firing the ultimate weapon, and ending up in the game's world. He will then have the player push one of two buttons, one which activates the ultimate weapon, and one which opens the path to Giovanni. The ultimate weapon is activated regardless which button the player chooses, but after defeating Lysandre, the player can press the other button and deactivate the weapon.
In the anime
In Pokémon Generations
The ultimate weapon was featured heavily in The Redemption through flashbacks. The weapon's backstory was detailed, showing AZ building it to revive his lost Floette, granting himself immortality in the process. He was later seen converting it into a weapon to destroy both sides of the great war, finally bringing it to an end.
In the manga
In the Pokémon Adventures manga
The ultimate weapon in Pokémon Adventures
In the X & Y chapter, the ultimate weapon is sought after by Team Flare, who plan to unleash its power onto the Kalos region. The machine contains an Absorber (Japanese: 吸収盤 Absorber) that can drain the life force of Pokémon.
Team Flare's plan consists of capturing the Legendary Pokémon Xerneas and Yveltal so that they can drain their energy to power the machine. The two Legendary Pokémon are summoned to Vaniville Town, where they battle each other and cause panic and destruction to the unsuspecting townspeople. Team Flare watches the destruction from afar, but Xerosic notes that they have no actual methods of capturing the two Pokémon. Later, the two Pokémon end their battle and leave to parts unknown. Xerosic later finds the dormant tree form of Xerneas at Route 8. By using the captured Vaniville townspeople as mind-controlled slaves, Team Flare manages to take Xerneas to their base. After hooking the tree to the Absorber, Lysandre begins the process of absorbing Xerneas's energy.
The Absorber in Pokémon Adventures
X later travels to the Team Flare Secret HQ to stop Team Flare's plan. After arriving at the ultimate weapon's control room, he battles Lysandre. X's attempts to stop the weapon from being activated end in his defeat, but he causes Xerneas to awaken. When X's friends arrive at Geosenge Town, they find the ultimate weapon emerging from underground. They attempt to keep the weapon from opening, but it still manages to fire on the Kalos region. Despite this, the combined efforts of X and his allies drained the weapon of enough power that no innocent lives were taken.
Later, Xerosic discovers that the stones on Route 10 are actually an ancient form of the Absorber used by AZ when he first used the ultimate weapon. Due to Xerneas destroying the Absorber when it awakened, he decided to use these Absorbers in place of the previous one. Team Flare gathers multiple Pokémon from the Pokémon Village to act as the power source, but are defeated by Clemont, Bonnie, Viola, and Yvette before enough energy can be gathered for a second attempt.
The flower in Pokémon Adventures
In the Omega Ruby & Alpha Sapphire chapter, two more Absorbers appear under the possession of the Devon Corporation. The Absorbers are taken to the Sea Mauville, where Mr. Stone and Steven Stone use them to drain the life force of Chic and Sceptile in their Mega-Evolved states so that the energy can be used to power a machine that will transport an incoming meteoroid that threatens to destroy the planet.
A smaller, portable version of the Absorber is seen in video footage contained at an old Pokémon Association science facility. This machine, nicknamed the "flower" (Japanese: 花), is a small cannon-like device with the barrel shaped like the ultimate weapon. This device was used in an attempt to drain Rayquaza of its life energy in order to weaken and capture it for the Pokémon Association at the Embedded Tower.
In other languages