There is a side quest that can be completed as you progress through Memoria. Check out the Nero Family side quest page for more information.
This side quest is entirely optional and the reward (a 
Protect Ring), while relatively strong, is not unique and you likely already have one in your possession.
It can be easy to lose your place in Memoria. Open up the Menu Screen and look in the bottom-right corner to check which room you are in and to ensure that you are in the correct place according to this walkthrough.
Memoria can be accessed by traveling to the Iifa Tree, but there are some preparations that you may want to make before entering. For starters, equip your characters with any Wind-resistant equipment they may have as a primary means of defense for an upcoming fight. Secondary to Wind-resistance, focus on Water-resistant items and equipment.
Ribbons work very well as they absorb both Water and Wind Elem-Atk (and you should have three at this point if you have been following the strategy guide all the way through). Protect Rings also work fairly well as they reduce all elemental damage by 50%. Also make sure that Zidane has the 
Master Thief Ability equipped.
Fly the Invincible straight into the purple orb when you are ready to proceed.
Level: 67
HP: 54,940
Start having Zidane attempt to Steal items as soon as the battle begins. The 
Dragon Wrist is nice, but the 
Grand Armor that the Nova Dragon holds is a fantastic piece of equipment that is difficult to obtain elsewhere in the game.
It is also listed as a “Very Rare” steal item, which means you will have to get very lucky in order to successfully steal it. Don’t hold up the fight trying to get it but you should have Zidane steal throughout just for the shot at it.
Nova Dragon will use a number of Wind-based attacks including Aerial Slash and Twister which you should be familiar with - they will hit all four of your party members. It will also use a move called Tidal Wave to inflict Water-based damage to all party members. Assuming that you have a few Ribbon items equipped you should have no problem weathering the storm of attacks while Zidane focuses on Stealing.
The dragon is also susceptible to Silence, Darkness and Sleep which can all be inflicted if you are having trouble withstanding the attacks.
Steal:
Remedy (common)
Dragon Wrist (uncommon)
Grand Armor (very rare)
Drops:
Wing Edge (common)
Ether (uncommon)
Elixir (rare)
There is a short cutscene at the entrance to Memoria where Zidane will speak to Garland. Choose your party members and then proceed up the steps towards the large castle.
Save your game and use a 
Tent at the strange looking multi-colored orb at the top of the steps. Search the right side of the screen for a hidden treasure chest that contains 
Kain’s Lance.
Kain’s Legacy
Obtaining Kain’s Lance will automatically reward you with the Kain’s Legacy Trophy.
This is a fairly strong weapon for Freya but it is not stronger than Dragon’s Hair. Either way though, you may wish to equip is though so that Freya can learn the 
Dragon’s Crest and Cherry Blossom Abilities. Continue along the pathway and out the back of the room.
There is an invisible character called the Master Phantom on the left side of the entrance that you can interact with by pressing the 
Button and challenging him to a game of Tetra Master. Master Phantom has a number of high level Tetra Master cards that you can win by challenging him to a match. Follow the stairs around and into the next room.
Follow the pathway up the stairs to the left. There is a small platform that extends outwards towards the screen. Examine near the edge of it until a Field Icon appears.
Open it to obtain 
The Tower which is a relatively strong weapon for Zidane but certainly not stronger than Ultima Weapon if you managed to obtain it during the Chocograph side quest.
Close But No Cigar
Obtaining The Tower will automatically reward you with the Close But No Cigar Trophy.
There is a boss in the next area that you are about to face that has a number of Fire-based attacks. Equip items that absorb or resist Fire-based attacks such as 
Rosetta Ring and equip the Body Temp in order to prevent the Heat negative status effect.
Proceed to the next screen and along the Outer Path when you are ready and the boss battle will automatically initiate when you reach a certain point along the pathway.
Level: 72
HP: 59,497
This is the boss that Amarant and Freya dealt with at the Fire Shrine during the Shimmering Island sequence.
Most of Maliris’ attacks are Fire-based. It will cast Firaga and Flame Slash which both do Fire-based damage to a single party member. It also has a move called Sword Quiver which is just physical damage to all party members.
Lastly, it will use a move called Mustard Bomb which will inflict the “Heat” status affect to any character that does not have the Body Temp Ability enabled. Doing any actions while afflicted with the Heat status affect will instantly KO that character. Skip their turn until the status effect can be removed.
Zidane can use his Soul Blade attack on Maliris and if he has his Ultima Weapon equipped it will automatically inflict the Sleep status effect, allowing you to Steal all three items listed above and easily finish the fight.
Maliris will use a move called Raining Swords at the end of the fight that hits each party member for 500-1,000 damage so make sure you keep all of your party member’s HP high enough to withstand it as you come towards the end of the fight.
Steal:
Genji Armor (common)
Ultima Sword (uncommon)
Masamune (rare)
Drops:
Phoenix Pinion (common)
Phoenix Down (uncommon)
Ether (rare)
Elixir (very rare)
Continue forward into the next room.
Move to the right side of the room and a cutscene will start once Zidane walks past the center pillar. The team will comment on how Memoria looks very similar to Alexandria and a short cinematic will take place as they observe out the window.
Walk up onto the platform at the end of the cutscene and inspect the right side to find a hidden Save/Tent point. Inspect the left side to obtain an 
Angel Flute for Eiko.
The Ultimate Flute
Obtaining the Angel Flute will automatically reward you with the The Ultimate Flute Trophy.
Continue up the stairs and into the next area where Zidane will comment on the rain. There is another hidden Tetra Master player known as the Defense Phantom on the left side of the screen at the top of the stairs.
Proceed across the bridge and another short cutscene will take place involving Zidane and Dagger discussing one of her memories. Go up the stairs and into the next area.
The next area contains a large set of stairs leading up to an eye in the sky. Search the left side of the screen to find the 
Rune Claws hidden behind the pillar. The Rune Claws are Amarant’s Ultimate Weapon.
The Ultimate Claws
Obtaining the Rune Claws will automatically reward you with the The Ultimate Claws Trophy.
Equip your characters with equipment that protects against Fire-based damage similar to before and Wind-based damage as well in preparation for an upcoming boss fight and that they all have the Body Temp ability equipped.
Make sure that Zidane has the Master Thief ability equipped to help him Steal some valuable items. Climb the stairs when you are ready.
Level: 72
HP: 59,494
Get Zidane to work on stealing the items, but be aware that the 
Grand Helm is incredibly difficult to successfully steal.
Tiamat is one of the more difficult fights in Memoria. His attacks include Absorb MP which drains MP from a single party member, Absorb Magic which lowers Magic stat of a single party member, Absorb Strength which does the same but for the Strength stat, Twister which inflicts Wind-damage to all party members, Silent Claw which does some physical damage and can inflict the Silence status effect, Jet Fire which does Fire-based damage and can inflict the Heat status effect and “Snort” which removes a character from the battle.
Snort is the most devastating attack as it permanently removes a character from the battle, but Tiamat will only use Snort as a counterattack and on a character who is floating. The best way to avoid the use of this move is to either avoid attacking Tiamat while a character is floating and wait it out or cast Dispel and remove the status effect.
Tiamat is susceptible to the Sleep status effect though, so have Zidane use the Soul Blade ability and (assuming he has his Ultima Weapon equipped) it will automatically put Tiamat to sleep.
Steal:
Blood Sword (common)
Feather Boots (uncommon)
Grand Helm (very rare)
Drops:
Wing Edge (common)
Phoenix Down (uncommon)
Ether (rare)
Elixir (very rare)
Continue down the pathway through the ruins and into the next area (“Lost Memory”). There is another hidden card player here called Strong Phantom that you can challenge to a game of Tetra Master.
Go straight through the next room (with the bells) and follow the bridge up the left side of the screen. Another short cutscene will take place with Zidane observing Terra and Gaia smashing into one another. Follow the pathway into the castle on the far side of the screen.
There is another colored orb that you can use to save your game and heal your characters with using a Tent. Note that this is the furthest you can go while still intending to complete the Nero Family side quest. Click on the link for more information.
You may run into an enemy called a Behemoth in this area. Those familiar with Behemoths in other Final Fantasy games in the series will recall how dangerous they are. Behemoths will counter any physical attack with a move called “Meteor Counter” which will devastate your party member’s HP.
Use magical attacks (such as Vivi’s spells and Eiko’s Holy spell) and status effects on it, or just run away if you need to using Zidane’s “Flee” command. You can also cast Silence on it.
Continue forward in to the next area.
There is an optional boss named Hades that you can find in this ocean area. Defeating it will reveal the Master Synthesist which you can then use to synthesize high level items for you.
Begin by equipping any Water absorbing or resistant equipment. Check out the Master Synthesist side quest section for more information:
You may wish to go back and save afterwards if you did battle and defeat Hades. Continue through the ocean room and into the next room for a short cutscene where the team discusses how Gaia used to be fully covered in water.
There is an upcoming boss fight at the top of the stairs. You should prepare by equipping each of your characters with armor and accessories that absorb or resist Water-based magic attacks. The Ribbon accessory works exceptionally well here again with the Protect Ring working as a half decent substitute for those not equipped with a Ribbon.
Equip each of your characters with the Body Temp and Bright Eyes Abilities if they have them and then continue up the stairs.
Level: 72
HP: 59,496
Get Zidane started on Stealing the items that the Kraken is holding, specifically the 
Genji Helmet which are hard to come by.
Kraken has two Tentacles that join it in battle. The right one will use a move called “Water-gun” and the left one will use a move called “Ink” (which can potentially cause the Blind status effect). It can use a move called “Leg” which will inflict physical damage to one party member, “Freeze” which inflicts the Freeze status effect (which will cause a character to shatter if they are subsequently hit by a physical attack) which will not affect your party if they have the Body Temp Ability enables, and can cast Waterga.
This is one of the easier boss battles in Memoria and should not cause you too much trouble.
Steal:
Genji Helmet (common)
Wizard Rod (uncommon)
Glutton’s Robe (very rare)
Drops:
Phoenix Pinion (common)
Phoenix Down (uncommon)
Ether (rare)
Elixir (very rare)
Continue up the stairs and enter the next area.
This room has a large broken clock with a pathway leading around it. At the bottom of the stairs on the right side of the screen is a hidden Save Point / Tent Point that you can access.
There is also another hidden Rare Phantom at the top of the stairs in the area towards the back of the screen. You can challenge “the ghost of Card Master Empress…” to a game of Tetra Master to win some rare cards. Proceed west into the next room when you are ready.
Enter the large room and another short cutscene will take place showing the birth of Gaia. Climb the ladder up and into the next area. Search the left side of the platform to find the 
Mace of Zeus. This is Vivi’s strongest weapon which can teach him the Doomsday spell.
The Ultimate Mace
Obtaining the Mace of Zeus will automatically reward you with the The Ultimate Mace Trophy.
There is another Dark Phantom on the right side of the platform that you can challenge to a game of Tetra Master if you wish. Some preparation is required before you proceed up the ladder towards the next boss fight.
The next boss will cast a spell called LV5 Death which will instantly kill any character who is currently a level divisible by 5. You may want to engage in a couple more battles in order to level your characters until they are a level that is not divisible by 5, especially if you have more than 1 character who would be impacted by the LV5 Death spell.
Equip each of your characters with the Antibody and Locomotion Abilities and equip your characters with equipment and accessories that can either absorb or resist Earth-based attacks. Feather Boots, 
Circlets and 
Gaia Gear work extremely well.
Climb up the second ladder and go through the door at the top. Walk towards the doorways to initiate the next fight.
Level:71
HP: 58,554
Lich has the following attacks this go around:
Make sure that Vivi does not use his new spell, Doomsday, on the Lich. Focus on regular physical attacks while Zidane attempts to Steal all three items. There are no other surprises and this is a standard fight after those factors are considered.
Steal:
Genji Gloves (common)
Siren’s Flute (uncommon)
Black Robe (rare)
Drops:
Phoenix Pinion (common)
Phoenix Down (uncommon)
Ether (rare)
Elixir (very rare)
The game continues in a large room with some archways in space. Search the left side of the room to find a hidden Save/Tent space. This is also where you would obtain 
Excalibur II if you managed to complete that side quest.
Go through the gateway and into the next room when you are ready. There is another short cutscene before you reach the final area of the game.
