Emerald Weapon and Ruby Weapon constitute the two most challenging fights in Final Fantasy VII. Neither of them are required to complete the game - they are essentially an added level of difficulty for those who wish to continue playing and challenge themselves.
Defeating them is part of the Kalm Traveler’s side quests and the rewards that you get for defeating both Emerald and Ruby Weapon are fairly lackluster.
Overview of the Battle - What to Expect
The first notable aspect of the battle against Emerald Weapon is the small timer that typically appears in the corner during the fight. You can get rid of the timer by equipping one of your characters with Underwater Materia. Details on how to obtain Underwater Materia are included in the Kalm Traveler section.
This fight is all about preparation and the first step is understanding Emerald Weapon’s attack pattern and moves. Emerald Weapon has four “eyes” across the top of it that will change its attacks when they are open - you can hit the eyes once they open up. It will use the following moves during the battle:
Foot Stamp: Hits all of your characters for around 8,000-9,000 damage and can only be used when all of the eyes are closed.
Revenge Stamp: Similar to Foot Stamp but hits for much less damage.
Emerald Beam: Hits all of your characters for a fraction of their health and automatically dispels beneficial status effects including Regen, Shield, etc.
Emerald Shoot: Hits one of your characters for just over 9,000 damage and dispels beneficial status effects.
Aire Tam Storm: This move hits all of your characters. The damage is based on how much Materia each character has equipped and hits for 1,111 for each piece. This means that if you equip any character with 9 or more Materia this move will instantly kill them. For this reason, you should avoid equipping any character with more than 8 Materia total. (Note: Aire Tam is Materia spelled backwards).
Emerald Laser: Cast by the “eyes” when they are open. The blue eyes hit for damage while the orange eyes drain a character’s MP.
This battle is all about preparation. You need to make sure that your characters are fairly high leveled. They will need to be level 80 at a minimum. Check out the Leveling Your Characters section for more information on how to level your characters up quickly. Each of your characters will need to have 9,999 HP with a minimal amount of HP Plus Materia added. Other Materia to equip includes:
Knights of the Round Materia (MASTERED): This will be your primary attack against Emerald Weapon as it is capable of doing the most amount of damage. Check out the Chocobo Racing and Breeding section for more information on how to obtain this Materia. Note that the damage Knights of the Round Materia does is based of your character’s Magic stat, so it can be beneficial to equip Magic Plus Materia. You may need to keep leveling your characters if Knights of the Round isn’t doing 8000+ damage per hit.
W-Summon Materia: This Materia will allow a single character to cast the Knights of the Round summon twice in a row. Make sure that you equip it to the same character that you equip Knights of the Round Materia to.
Mime Materia (MASTERED): This Materia can be retrieved from one of the Materia Caves. You need to master it in order to create a second copy of Mime Materia so that both of your characters who do not have Knights of the Round / W-Summon both have a Mime Materia. Check out the Leveling Your Materia section for more information on how to level it up as quickly as you can.
Final Attack Materia and Phoenix Materia: This pairing acts as a safety net - one which you will most likely need to utilize in order to defeat Emerald Weapon. This pairing will cause a character that dies to summon Phoenix as their last move which will instantly revive (and any other killed party member) back to full health. Check out the Battle Square section for more information about how to find a Final Attack Materia.
Underwater Materia: Don’t forget to equip an Underwater Materia to one of your characters before the battle.
You can fill the remaining eight slots for each character with any other Materia that you like. You will earn a ton of AP once you defeat Emerald Weapon, and while you will likely have most of your Materia fully leveled up and mastered at this point in the game, make sure that you equip any of your Materia that is not fully leveled up to a weapon or armor that has at least regular growth. Equipping Materia to your Ultimate Weapons will cause you to miss out on the AP.
Make sure to charge up Cloud’s Limit Break gauge so that he can also take advantage of using Omnislash during a lull between Knights of the Round castings.
Emerald Weapon can be found swimming in the waters around the Underwater Reactor. There are a few random places that it can appear - just surface the submarine and submerge again and it will reappear in another location.
Have the character that has the W-Summon Materia and Knights of the Round Materia cast the Knights of the Round summon twice and then have both of your other characters use the Mime command. Be careful not to use Omnislash or another Limit Break in between as the next character will attempt to mime Omnislash and will be unsuccessful. Use up your Megalixirs during this battle as you need to and avoid casting protective spells and beneficial status effects as most of Emerald Weapon’s attacks will remove them automatically.
Emerald Weapon has 1,000,000 HP and it will take several rounds of summoning and Limit Breaks to bring it down.
The reward for defeating Emerald Weapon is the Earth Harp which can be traded to the Kalm Traveler back in Kalm for three Master Materia: Master Command Materia, Master Magic Materia and Master Summon Materia.