The Mission Continues is a quest in Final Fantasy VII Rebirth, taking place in a flashback of the Nibel Region during Chapter 1, "Fall of a Hero". It has the subquests Up the Cliff, Beware the Gas, Unlock the Elevator, and Short Power Cord. 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. As the bridge to the Nibel Reactor collapsed, the group were forced to take an alternate route.
Walkthrough[]
Sephiroth joins the party as a playable member. His materia and equipment cannot be changed, but what he has equipped grants him access to a vast number of powerful spells, allowing him to cast powerful magic damage to all opponents.
Sephiroth's moveset is the same as when he was briefly controlled in "Home Sweet Home", where Aura Change grants him new unique abilities based on battle progression. He is an agile melee fighter and his two character abilities are Hell's Gate, where he jumps and slams and area-of-effect attack (and can follow it up with the unique ability Infernal Gate), and Zanshin, where he launches waves of energy at enemies. Between these and his spells from equipped materia, he is incredibly powerful.
Having Sephiroth in the party also grants access to synergy skills and a synergy ability. Synergy skills can be used any time in battle, while synergy abilities can be used after both party members have used a requisite number of ATB commands. The synergy skill Voidshatter grants great damage but is slow to charge, and can be used often in combat, while Dualblade Dance can deal quick damage. The synergy ability Double Helix will deal immense damage and grant Sephiroth unlimited MP after use, meaning he can cast even more frequently.
Up the Cliff[]
Climbing the cliff will lead to an area with a rest stop, and a battle with three insectoid chimera. These are even simpler to beat with Sephiroth also in the party, and after they are defeated, an 
HP Up Materia can be picked up, a useful equip for Cloud to boost his HP. After this, head forward into the cave.
Beware the Gas[]
Upon entering the cave, hug the right wall and keep going over the tree until an 
Empowerment Materia is found. This grants spells 
Bravery and Faith that boost offensive attributes temporarily in battle, and can potentially be used to boost Sephiroth's attack power. After obtaining it, head back toward the path and defeat the velociwings encountered here. This will lead to a mako spring, where a cutscene commences.
Following the cutscene, head down the cave to the right where a screamer and velociwing are encountered. When they are defeated, head right onto the small cliff for an 
Spare Change Materia (this grants an ability that throws gil for damage, but is very inefficient for its limited damage output; however, as nothing carries to Chapter 2, the player is free to expend all their funds here), and then keep following the path ahead. The path has more encounters, most of which are repeats of previous enemies, aside from Twin Brain. Twin Brain is capable of using Screech to stun a target, and Life Siphon to drain HP; if these attacks are avoided, it is defeated easily as it lacks durability.
Further along the path are wooden planks along a cliff. After crossing them, dropping to the left is a 
Magnify Materia, which allows the linked Magic Materia to target multiple targets. This can be useful for either Healing Materia for Cloud to heal both him and Sephiroth at once, or with an offensive magic to hit multiple enemies.
After reaching facilities just below the reactor, a zu is fought. This is a flying enemy which uses both ranged and melee attacks, and is durable. It is weak to 
Wind, meaning using Aero (granted from the Wind Materia) is a great way to damage and stagger it to defeat it. Climb the stairs ahead, grabbing the 
Mega-Potion in the chest on the right and the Precision Defense Focus Materia on the ledges on the left on the way. Precision defense focus makes it easier to fully block an attack by increasing the window allowed after guarding where an attack will be blocked completely, and can come in handy as a means of defense.
Keep following the path battling enemies along the way and reaching a long ladder. After climbing the ladder, immediately up steps on the left is an Auto-Cast Materia, which will cause a non-controlled party member to cast spells from a linked materia on their own (since only Cloud can be controlled here, this should be used only if players prefer Sephiroth, and is not ideal for now as materia slots are precious).
Unlock the Elevator[]
Further up yet another long ladder is an unusable elevator. To the right, is Comet Materia. This casts powerful, but also incredibly costly spells; though they can be experimented now during this flashback, Cloud's limited MP makes doing so a risky use of a materia slot.
Unlocking this elevator is the same as in the previous quest, where one must use the mako processing unit to clean up the gas. The short cord it is attached to makes this one less straightforward. First, pull the unit past the fence to get the closest gas cloud, then pull it around where its cord leads from. Pull the switch to open the large door, then pull the unit through to get the other gas clouds.
After unlocking the elevator, use it and follow the path ahead. Two Elixirs can be found in chests nearby (one just to the left of the entrance, another down a ladder to the right), and a bench next to the ladder can be used for a much-needed rest stop. Past this, through a door, a cutscene takes place and leads to the boss.
Materia Guardian boss[]
Materia Guardian is capable of using ranged attacks, such as its Mucous Discharge, where it spits acid, as well as Seizing Claws, in which it grabs a party member, disabling them temporarily. Materia Guardian is weak to 
Fire, and its weak points are its legs, which can be damaged to cripple its movement, or to free a seized ally.
It is ideal to dodge its Seizing Claw attack, using Sephiroth's mobility or Cloud's ranged attacks. Using Fire, especially on its legs, can be very effective, while Sephiroth can, if he builds up two ATB gauges, use Firaga for even greater damage. This can help stagger it to have a chance to deal immense damage. After a certain amount of its HP is gone, it will cling to the ceiling, requiring Sephiroth or Cloud to aim for its legs with fire spells.
It is important to use ATB commands on both party members, mixing attacks and fire spells, so that Double Helix is available. Doing this will not only deal great damage to Materia Guardian, but gives Sephiroth free MP, so he can cast Firaga after building up ATB charges with no drawbacks.
On 25% HP, Materia Guardian will begin to cast Trine, a powerful spell. If they become available, limit breaks are free to use and deal strong damage while rendering the user invulnerable during their use. Saving them for Trine will enable Cloud or Sephiroth to avoid Trine's damage entirely (as it could potentially kill them); otherwise, simply heal to full HP to be able to take the hit.
After Materia Guardian is defeated, another scene leads to the next quest, "Reactor Survey".
Hard mode tips[]
Though most regular enemies are more challenging, Cloud will have his full materia setup from the normal playthrough, making them relatively straightforward. Against Materia Guardian, Cloud can pair fire with Elemental Materia to avoid most damage. Materia Guardian's greater durability makes it more important to save a limit break to avoid Trine's damage.