Sector 1 Reactor The Sector 1 Reactor is one of the eight Mako Reactor s built by the Shinra Electric Power Company to power the city of Midgar , appropriately found in Sector 1 , in " Final Fantasy VII " . Its layout is the same as the Sector 5 Reactor . The Sector 1 Reactor is the northernmost reactor in Midgar , and is even referred to as the " Northern Reactor " . Story . The eco - terrorist group AVALANCHE , in an attempt to save the Planet from the corrupting ways of Shinra , attacks the reactor . The effort is led by Barret Wallace who is accompanied by Biggs , Wedge , Jessie , and the recently hired mercenary Cloud Strife . The team captures a train and uses it to break into the reactor grounds , which are defended by Shinra guards . The team fights its way down into the main generator , and prepares to put the charges in . Cloud has a brief flashback to the incident in Nibelheim and suffers a psychic disturbance . Before the charges can be pulled , the robot Guard Scorpion attacks , and is defeated by Cloud and Barret before they and the rest to AVALANCHE make their way back out before the reactor explodes . The explosion causes massive destruction with unknown numbers of civilian casualties . Cloud and AVALANCHE scatter to regroup at the train heading for the Sector 7 slums . The reactor remains closed , and when Shinra places the Sister Ray cannon within Midgar , seven reactors charge up its blast , Sector 1 Reactor still out of commission . Locations . Entrance . The entrance is a metallic , brown - ish area full of large pipes , rusting doors and machinery . It is a set of joined rooms with terminals , though aside from a treasure chest , has little of interest to the player other than dialog interactions . At the northeast - most location , the player can access the elevator . Elevator . When accessed , the elevator only contains a small space , with a button to press for it to either ascend or descend . On the first ascension up using the elevator , dialog between Barret and Cloud initiates . Main Staircase . The main staircase is a large , expansive room , with a red tint on the stairways , dark brick walls and metallic pipes . Here , the player must descend the stairs down to a door at the bottom , which leads to the upper piping area . Later , the player must ascend to escape the Reactor . Upper Piping . A damaged area , the upper piping is full of rusting metallic tubes . The player must cross the brick surface to the ladder , in order to climb below to the lower piping , and later ascend to escape the Reactor . Lower Piping . Similar to the upper piping , this is a metallic area with ladders and pipes that the player must descend in order to reach the core , and later ascend to escape the Reactor . Core . The core is a large expansive area with only a single walkway leading towards it , surrounded by metallic pipes and heavy machinery . Here , a cutscene initiates , and the first boss of the game , Guard Scorpion , is fought . Following this , the detonator will set , and the player must run to escape its explosion . Quests . Destroying the Reactor . The first quest in the game , Cloud and Barret begin at the Entrance , where Biggs and Jessie allow them to enter through the doors to the elevator , which Jessie operates . Following this , they must descend down through the staircase , the pipes and finally reach the core . A timer initiates , and Guard Scorpion must be fought to proceed . After this , the two must run back beating the time , rescuing Jessie along the way up the pipes , and finally escaping the Reactor before being caught in the explosion . Musical themes . On the reactor grounds " Opening - Bombing Mission " plays . The theme has been remixed several times , and also appears in " Crisis Core - Final Fantasy VII - " . " " plays inside the reactor itself until the Guard Scorpion battle begins , where the background theme changes back to " Bombing Mission " . Other appearances . " Final Fantasy VII " Demo . The Sector 1 Reactor bombing mission is the setting for the two PlayStation demos of " Final Fantasy VII " . Two versions of the demo exist , often differentiated by the third playable character : Aeris or Tifa . The Aeris demo is of earlier build and still has many changes from the final version . The Tifa demo is closer to the playable segment in the full game . In the final game of course , neither girl is playable , and only Cloud and Barret are in the player ' s party . Both demos end when AVALANCHE escapes the exploding reactor . " Final Fantasy Record Keeper " . Mako Reactor No . 1 is the first dungeon available whose completion unlocks Mako Reactor No . 5 in the " Final Fantasy VII " realm .