Sister Ray The Sister Ray , originally called the Mako Cannon , is a huge weapon built by the Shinra Electric Power Company in " Final Fantasy VII " . Its power is originally run by Huge Materia , though later it is moved to Midgar so that it can be powered by the city ' s Mako reserves . The cannon ' s blasts of energy are powerful enough to destroy entire cities or Weapons , and can cover massive ranges while retaining their strength . Story . Junon . 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 ' s 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 a scapegoat for the crisis the Planet is embroiled 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 . Midgar . After the near - disaster in Junon , the cannon is moved to the capital city of Midgar where its power is boosted by the combined charging power of the city ' s entire electrical power grid as the Mako Reactor s around the city are hooked up to the cannon . Specially designed to destroy the force field around Sephiroth ' s base in Northern Cave 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 as the " Sister Ray " . A second Weapon appears out of the ocean , the Diamond Weapon ; it comes out of the seas below the Forgotten Capital 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 the windows of Shinra Headquarters shatter and parts of the cannon itself dislodges and falls to the ground . With one blast , the Sister Ray fatally wounded the weapon and destroyed Sephiroth ' s barrier . With Diamond Weapon ' s final attack destroying the top floors of the Shinra Building , with Rufus presumed dead , Midgar descends into chaos and various Shinra factions fighting for control while Professor Hojo takes position at the Sister Ray ' s controls . Hojo ' s scheme is to fire the cannon one last time 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 . Destruction . The Sister Ray is destroyed along with most of the Midgar in the cataclysm of Meteor falling on the city and its ruins can be seen in " " . 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 . Etymology . The cannon may have been named after a song by , featured on their " White Light / White Heat " album .