The cannon was originally installed in Junon. In Crisis Core -Final Fantasy VII-, it appears in a flashback as a virtual battle ground for Sephiroth, Angeal Hewley and Genesis Rhapsodos. The battle is intense enough that most of the cannon is sliced off into the sea. However, it is just a simulation.

In Final Fantasy VII the cannon can be seen as the party first travels through the city, but it is not used until after the emergence of Weapons following Sephiroth's summoning of Meteor. When Tifa and Barret are kidnapped by Shinra to be used as scapegoats for the crisis the planet is in, Tifa is thrown into a gas chamber to be executed. The plans are ruined when the Sapphire Weapon charges at Junon from the sea.

The first firing of the cannon is ineffective, and the Weapon's counter-attack blasts a hole in the fortress's armor. The Weapon charges a second blast, but the second firing of the cannon at point-blank range destroys it. Tifa escapes the gas chamber through the hole the Weapon blasted and runs onto the cannon's barrel. After a brief slap-fight with the Shinra executive Scarlet, Tifa escapes onto the Highwind.

Later, when the party arrives in Junon to get the Huge Materia from the Underwater Reactor, the cannon has disappeared. Cloud takes note by stopping and mentioning that something is missing.

After the near-disaster in Junon, the cannon is moved to the capital city of Midgar, where its power is boosted by the mako reactors around the city. Specially designed to destroy the force field around Sephiroth's base within the North Crater, President Rufus Shinra puts the hopes of the survival of the planet—and his company—on the cannon. Scarlet dubs the modified cannon the "Sister Ray".

A second Weapon emerges from the ocean, the Diamond Weapon, and makes a beeline for Midgar. Despite the party's attempts to defeat it, the Weapon continues its advance towards Midgar. The Sister Ray is fired with such force that the windows of the Shinra Building shatter and parts of the cannon itself dislodge and fall off. With one blast, the Sister Ray fatally wounds the weapon and obliterates Sephiroth's barrier.

Diamond Weapon's final attack destroys the top floors of the Shinra Building and Rufus is presumed dead. Midgar descends into chaos, with various Shinra factions fighting for control while Professor Hojo takes over the Sister Ray's controls, his scheme to fire the cannon again to give his son, Sephiroth, more power at the potential cost of Midgar from the system overload. The plan is foiled when Hojo is killed by Cloud's party.

The Sister Ray is destroyed along with most of the Midgar when Meteor falls on the city. Its ruins are seen in Final Fantasy VII: Advent Children. In the opening movie of Dirge of Cerberus -Final Fantasy VII-, just before the destruction, Vincent Valentine spots Hojo at the controls of the cannon, thinking it to be just an illusion.

