The Mission Begins, Happy Trails, Clear the Way, Bridge is Out, and Cross the Bridge are quests in Final Fantasy VII Rebirth, taking place in a flashback of Mt. Nibel during Chapter 1, "Fall of a Hero". Cloud Strife in the present day narrates a tale in which he and Sephiroth, accompanied by two soldiers and guided by Tifa Lockhart, traversed Mt. Nibel to reach the Nibel Reactor. The route took them through some buildings around the mountain, toward the bridge leading to the reactor.
Walkthrough[]
This quest will involve combat as Cloud Strife, the only playable party member. All materia used and gained here is limited to the flashback. The materia Cloud comes pre-equipped with allows him to use magic, and grants other enhancements.
Cloud's unique ability is Punisher Mode, which allows him to toggle between two stances: Punisher Mode and Operator Mode. Punisher Mode deals greater damage and allows him to counter melee attacks, but is much slower and cannot guard ranged attacks, while Operator Mode deals less damage but offers much greater movement. In Operator Mode, Cloud can use ranged attacks by dodge-rolling and attacking.
Cloud's other character abilities are Braver (a single strong physical attack for pure damage), Focused Thrust (a forward physical attack that raises stagger quickly), and Triple Slash (three attacks in succession). Triple Slash is an excellent means of spreading out damage and also granting mobility for Cloud, while Focused Thrust comes in handy against larger enemies so as to stagger them, and Braver can deal great damage in one move.
The Mission Begins[]
Follow Tifa along the mountain path until encountering two insectoid chimera, where a battle begins after a brief cutscene. Their attacks are solely melee, meaning Cloud can use Punisher Mode to deal area-of-effect damage against them and to counter-attack them with ease. They are also weak to 
Ice, but there is no need to expend magic here. Triple Slash and his other abilities are similarly effective.
After this battle, players who have completed the Final Fantasy VII Rebirth demo have the option to skip until "Sephiroth's Whereabouts".
Happy Trails[]
Further up the mountain, kyuvilduns are encountered. These are smaller enemies that insectoid chimera but more mobile, and are melee based. They similarly can be dispatched quickly with Punisher Mode attacks and Triple Slash.
After defeating them, head further up and cross a bridge, where a brief cutscene takes place followed by a battle against a velociwing. This is a more powerful flying opponent, which is more durable, and uses ranged and melee attacks. These attacks are telegraphed with their animation and, in Operator Mode, can be blocked with a perfect block if timed by guarding just before the attack lands. It is better here to use a mix of ranged attacks, melee attacks, and Triple Slash instead, as its durability makes this more challenging. If the velociwing is staggered or grounded, Punisher Mode can finish it off.
Defeating the velociwing and heading forward will lead to a second velociwing accompanied by a kyuvildun. After beating them, a cutscene will commence followed by a brief battle against two more velociwings, followed then by another cutscene and then the next segment.
Clear the Way[]
The previous battle granted an 
Assess Materia, which can be useful to discover the attacks and weaknesses of enemies. After equipping, travel along the linear path up the mountain, where enemies are encountered along the way (though these are the same as previously fought). Along the right side of the path are treasure chests with two 
Mixed Hi-Potions. On the left side of the path further along is a 
Wind Materia, which allows the user to cast offensive wind spells (and may be helpful later).
Reaching the end of the path, Tifa will call out to Cloud that it is a dead-end, leading to the next portion.
Bridge Is Out[]
New Route[]
Return to Tifa and follow her through the narrow gap, then further on the path into the mako measurement facility. Climbing the stairs inside, on the right is a 
Level Boost Materia, which boosts the level of the paired materia, unlocking spells or upgrades from when the materia has leveled up. This can be paired effectively with Healing Materia to heal better, or with an offensive materia to deal more damage.
Continue inside and use the facility's first elevator. A screamer is fought here, which is a much more durable enemy that uses strong spinning melee attacks but is slow. Using Punisher Mode, Cloud can guard against its attacks and counterattack to great effect, especially if followed up with Focused Thrust to eventually stagger it. Alternatively, with Fire Materia equipped, casting 
Fire or Fira can deal great damage and pressure it.
After defeating the screamer, head to the path where it came from, head right over the barrier, and down the path to find a chest with an ether. To proceed, head up the stairs to the next segment.
Unlock the Elevator[]
The elevator is unlocked by using the nearby mako processing unit. Approaching and drag it over to the pockets of mako gas to clean them up. Once all mako gas is removed, the elevator can be taken upstairs.
Cross the Bridge[]
After taking the elevator to the southern ridge summit, head forward along the linear path. After reaching a heli-pad and viewing the brief cutscene, head right through the open gate to find a chest with an Elixir before then resuming the path. At the end of it, crossing the bridge will lead to a cutscene and then the next quest, "The Mission Continues".
Hard mode tips[]
When revisiting the quest for hard mode, Cloud retains all materia that he would have had in other chapters. The quest is otherwise unchanged.