Enter the Reactor Grounds (侵入路を進む, Shinnyūro o Susumu?, lit. Proceed through the Invasion Route), Infiltrate the Reactor, and Follow Barret (バレットたちに続け, Baretto-tachi ni Tsuzuke?, lit. Follow Barret and the Others) are the first quests in Final Fantasy VII Remake, taking place in Mako Reactor 1 at the start of Chapter 1, "The Destruction of Mako Reactor 1". Cloud Strife is hired to defeat the Shinra Electric Power Company's defenses, and create a safe path for Avalanche to breach through and destroy Mako Reactor 1.
The quest begins as soon as the opening movie finishes. When entering the Platform, the cast jump off of the train to the platform and knock down two Security Officers. As Avalanche's hired mercenary, Cloud jumps off the train and follows their lead.
Walkthrough[]
Enter the Reactor Grounds[]
Train Station.
Upon gaining control of Cloud, heading north past Barret causes two security officerss to appear. Both enemies are easy to defeat with simple attacks. Defeat the guards, after which Cloud will level up to 7. After this, continue heading north of the platform and turn left to enter the station, where a fight against another pair of officers commences and the tutorial on the ATB gauge and commands appears. 
Fire is a spell that deals strong damage of the 
Fire element, which the soldiers are weak to, and helps stagger a stronger enemy, but costs MP to cast. Focused Thrust deals damage and builds the enemy's stagger gauge faster, while Braver deals stronger damage. The Security Officers will be defeated quickly regardless of which ability is used.
Next, head inside the main area to fight three officers. After defeating the troops, head upstairs, and then open the chest in front of Cloud to obtain two potions. Two grenades can be obtained in a chest by turning left and head to the small area behind the staircase railing and opening the chest located beside a "Clear Icicle" vending machine. After this, head out into the balcony of the upper station area and destroy the set of boxes to the right (which may yield a Moogle Medal) and another set in front of Wedge. These boxes may yield a potion, a mako shard (restores MP when collected), both, or neither.
Approach Wedge and Cloud will get acquainted with the team and to proceed to the Reactor Grounds. After approaching Wedge, a short scene will commence, after which Biggs and Jessie will exchange dialogue while working on the door. Head right and approach Barret for another scene to commence, following which the door opens. This leads to the next quest.
Infiltrate the Reactor[]
Once inside the compound, head towards the enemies: one Security Officer and one Guard Dog. The Guard Dog has more HP; use normal attacks on the Officer to build the ATB gauge, and then unleash Fire or Focused Thrust to stagger the Guard Dog, then pummel it with attacks or Braver. A bottle of ether can be found by heading north towards a short alleyway to open a chest. Next, head towards a warehouse on the east, where Cloud is called out by Wedge to catch up. This leads to "Follow Barret".
Follow Barret[]
Ride an elevator to get to the upper level of the warehouse, and turn left, leading down a ramp. To the left of the ramp are two Shinra boxes. When following after the group, Biggs informs Cloud of the enemies, consisting of two Security Officers and one Guard Dog, behind him. The same strategy against these applies; attack the Security Officers with normal attacks, and use ATB commands first to stagger the Guard Dog and then destroy it with commands and attacks. Following the battle, use potions to heal.
Next, head through the gap in the fence, and follow the path to the end, at which is a group of Security Officers. After defeating them, a chest containing two potions is located in front of the forklift can be opened. Proceed through a narrow yet tall hallway, and hold 
to pull the switch and open the door to a walkway. Wedge stands at the left end of the walkway to secure the group's escape, while Cloud must head right to join Barret, Biggs, and Jessie inside the reactor.
The chapter continues in the next quest, "Breach Security".
Hard mode tips[]
When replaying the quests on Hard Mode, Cloud can make use of Triple Slash often to more quickly defeat the security officers. Cloud can equip 
First Strike Materia to open many battles with this ability and end fights quickly. Because items cannot be used in Hard Mode, forgo any treasure chests and focus only on smashing crates.