Sidequest

Sidequests are completely optional, mostly non-storyline objectives the player can undertake throughout the game, and has been predominant throughout the series. Sidequests can range from something as little as an errand or finding an item to something as big as traveling over the world for many various objectives or fighting superbosses. Several sidequests often involve getting powerful magic, summons, or equipment that would otherwise make the game extremely easy to complete.

Final Fantasy
The sidequests in this game were mostly about increasing your characters' capabilities.
 * Labyrinth of Time
 * Soul of Chaos
 * There is also a minor sidequest involving bringing Adamantite to a Dwarven smith to get the legendary sword Excalibur

Final Fantasy II

 * Arcane Labyrinth
 * Soul of Rebirth

Final Fantasy III

 * Odin can be battled if the player travels to the Saronia Catacombs when the Nautilus is obtained.
 * Leviathan can be found at Lake Dohr and can be acquired as a summon if the player defeats him.
 * Bahamut can be battled at Bahamut's Lair and can also be attained as a summon if defeated.
 * In Falgabard the player can fight Shinobi.
 * The Mognet sidequest in the Nintendo DS remake of the game gives the player access to the Optional Dungeon and Onion Knight job.
 * Sunken Cave is an optional area of the game

Final Fantasy IV

 * Odin - The player may challenge Odin in Baron once they have gone to the Feymarch. After defeating Odin in battle, the player will receive him as a summon.
 * Feymarch - Isolated on an island in magma in the Underworld. It is where the player may obtain several powerful equipment as well as the Avenger sword, and can challenge both Asura and Leviathan to a battle to obtain them as optional summons.
 * Lair of the Father - Accessed once the player can go to the moon. The player can engage Bahamut here once they have obtained Leviathan to try and obtain him as a summon.
 * Adamant Isle Grotto - Near Mythril Village, and the site of the Pink Puff Tail sidequest (and other tails in the DS version). Bringing a Pink Puff Tail will grant an Adamant Armor to the player. Bringing the Rat Tail will grant the player an Adamantite, which the player can use to obtain the Excalibur.
 * Sylph Cave - Found in the northwestern part of the underworld. The player can obtain the optional summon Sylph after they talk to Yang, return to Fabul and get the Pan, and then use the Pan on Yang. Returning the Pan to Fabul will also yield the Knife. This must be done before going to the moon for the first time.
 * Lunar Subterrane - Several optional bosses can be fought here for various powerful equipment, such as Ragnarok and Ribbon. The bosses include Dark Bahamut, Ogopogo, Lunasaur, Plague Horror, and White Dragon.
 * Lunar Ruins
 * Namingway
 * Proto-Babil
 * Geryon - After completing the DS version in the first playthrough, the player can challenge this new Boss in the "New game+" mode. It is found in Mount Ordeals.
 * Whyt

Final Fantasy IV: The After Years

 * The player can find tails throughout the game to exchange with the tail collector on the True Moon for powerful equipment. Adamantite can also be found and traded with Tradingway in the same location.
 * During Palom's Tale, the player can buy other membership cards to reach more levels of the club at Troia. This can earn the player Leonora's only whip, and the Black Tail.
 * Challenge Dungeons.
 * Omega and Lord Dragon are optional superbosses, and can earn the player the Hero Shield and Ragnarok after defeating them, respectively.
 * It's possible to miss some of the Eidolons in the Gathering Tale, which doesn't make them all necessary to advance further in the game. For example, Shiva can be killed on accident during the battle with her. The Chocobo is also a hidden Eidolon.

Final Fantasy V

 * Odin - Once again, the player may challenge Odin to obtain him as an optional summon. This can only be done in World 3, after climbing through Jachol Cave into the locked room in Castle of Bal.
 * Syldra - The player may obtain the optional summon Syldra in World 3 by returning to the Pirate's Hideout.
 * Catoblepas - Can only be done in World 2. The player may head to the northernmost area in World 2 (must have access to the Submarine to get to the area) and attempt to fight and defeat Catoblepas to obtain as an optional summon.
 * Shiva - In World 1, the player may attempt to defeat and obtain Shiva as an optional summon once they are able to go to Walse Castle and go through the hidden tower.
 * Bahamut - The player may return to North Mountain in World 3 to fight and obtain Bahamut as an optional summon.
 * Phoenix Tower - In World 3, the player may return to the desert surrounding North Mountain and head to the far southwest to reach Phoenix Tower, which comprises of 25 floors. At the top, they may obtain the optional summon Phoenix.
 * Fork Tower - After completing the Pyramid of Moore, the player may attempt to go to Fork Tower to obtain the spells Flare and Holy.
 * Istory Falls - The player may attempt to obtain a Lithograph as well as attempt to obtain the optional summon Leviathan.
 * Great Sea Trench - The player may attempt to obtain a Lithograph as well as obtain the powerful spell Meteor.
 * Gil Cave - The player may attempt to obtain lots of Gil, as well as attempt to fight the optional boss Gil Turtle.
 * Sunken Walse Tower - The player may attempt to reach and fight Famed Mimic Gogo to obtain the optional Job Class Mime.
 * Omega and Shinryu - The player may attempt to fight and defeat Omega and Shinryu in the Interdimensional Rift. Shinryu gives you the Ragnarok and Dragon Seal, while Omega gives you the Omega Badge and Dragon Seal.
 * Boco - In World 3, the player may attempt to go around the world with Boco to obtain the Magic Lamp, as well as win a Mirage Vest from a man in Phantom Village.
 * Carbuncle - The player may seek out and defeat Carbuncle in Castle Exdeath to obtain him as an optional summon.
 * Ramuh - In World 1, the player may fight around Istory in the forest to attempt to defeat and obtain Ramuh as an optional summon.
 * Golem - In Drakenvale, the player may help Golem by defeating the enemies attacking it to obtain it as an optional summon.
 * Sealed Temple

Final Fantasy VI

 * Deathgaze - In the World of Ruin, the player may attempt to fight and defeat Deathgaze for the Bahamut Magicite.
 * Eight Dragons - The player may attempt to seek out and defeat the Blue Dragon, Earth Dragon, Gold Dragon, Holy Dragon, Ice Dragon, Red Dragon, Skull Dragon, and Storm Dragon for various powerful equipment.
 * Crusader - By beating all of the Dragons (not the Dragon's Den version) and breaking their seal, the player may receive the Esper.
 * Dragons' Den - Only available in the GBA version. The player may attempt to defeat various powerful enemies, including the powerful Kaiser Dragon and Omega Weapon.
 * Dragon's Neck Coliseum - The player may attempt to win various prizes in a 1vs1 battle. In the GBA version, the player may also fight and defeat Gilgamesh and obtain him as an optional Esper. It is also possible to obtain Shadow here if the player did not leave him behind in the World of Balance.
 * Gau's Father - The player may attempt to seek Gau's past by adding Gau to the party and talking to the crazy old man. It could only be done in the World of Ruin.
 * Mog -or- the Golden Hairpin - After returning Terra back to her controlled state, the player could go to Narshe for the sidequest. It involves a wild goose chase of Lone Wolf the Pickpocket up to the cliff where Valigarmanda is settled. Then the player may choose Mog or the Golden Hairpin. As they choose one, the other choice falls down the cliff, and can never be retrieved, with the exception of Mog, who could be recruited in the World of Ruin.
 * Gogo - The player may attempt to recruit Gogo by going through a secret dungeon, after being eaten by a Zone Eater.
 * Umaro - The player may attempt to fight and recruit Umaro in the World of Ruin after they have recruited Mog.

Final Fantasy VII

 * WEAPONs - The player may attempt to fight and defeat the optional bosses Ultimate Weapon, Emerald Weapon, and Ruby Weapon for various prizes.
 * Ancient Forest - The player can reach Ancient Forest either by Green, Black, or Gold Chocobo or by defeating Ultimate Weapon. The player may then attempt to solve puzzles in order to obtain various powerful items and equipment.
 * Gold Saucer - The player may attempt to participate in various minigames, all of which can yield powerful equipment and items.
 * Chocobo Breeding - The player may attempt to breed different Chocobos of varying abilities to reach the Materia Caves, or to race in the Chocobo Square at the Gold Saucer.
 * Wutai - Before the raid on Midgar in Disc 2, the player may attempt to partake in this sidequest, in which the player must fight their way to Wutai to get their materia back. They can also, after completing the initial sidequest, attempt the Pagoda with Yuffie to obtain various prizes, including the Leviathan materia and Yuffie's ultimate Limit Break.
 * Yuffie - The player may attempt to recruit Yuffie by defeating the Mystery Ninja found in a variety of forests as early as the Junon Area, then answering the questions correctly.
 * Vincent - The player may attempt to recruit Vincent by defeating Lost Number to obtain the Key to Basement, finding his coffin, and speaking with him. The player must then go back through the caves to be stopped by Vincent asking to join the party.

Dirge of Cerberus -Final Fantasy VII-
This game varies( apart from the obvious game play differences) from the others in that it really doesn't have many, if any real side quests. Everything is accomplished via the missions that move the game forward.

You could claim that how you develop Vincent's weapon is a variant of sidequest.

Crisis Core -Final Fantasy VII-

 * Missions - There are over 100 missions that the player can participate in and takes the majority of the gameplay should the player participate in them all. Technically speaking, the missions are sidequests, though there are other side quests outside them. These are mostly in and under Midgar.

Final Fantasy VIII

 * Card Queen - Throughout the game, up to the end of Disc 3, the player may attempt this Triple Triad sidequest in which the player must lose various, specific cards to the Card Queen and follow her around the world to challenge various, specific people for extremely rare cards.
 * CC Group - Another Triple Triad sidequest that takes place after Balamb Garden is mobile, the player may find and play the various group members inside Balamb Garden to win rare cards.
 * Deep Sea Research Center - Once the player has access to the Ragnarok, the player may enter this optional area to fight and obtain the GF Bahamut, as well as return afterwards and try to reach and defeat the optional boss Ultima Weapon, from whom the player may draw the GF Eden from.
 * Obel Lake - The player may attempt to solve the riddle of Obel Lake to win a few special items, such as the Luck-J Scroll and Three Stars.
 * Shumi Village - Once the player has access to the mobile Garden, the player may attempt to head to the far north and enter the village to complete an errand quest for a few powerful items.
 * Winhill
 * Dollet
 * Centra Ruins - The player may attempt to reach the top of the Centra Ruins to challenge and defeat Odin to obtain him as an optional GF. In addition, the player may attempt to challenge and defeat the Tonberry King by defeating around 18+ Tonberries.
 * Jumbo Cactuar - The player may attempt to defeat and obtain the Jumbo Cactuar as an optional GF.
 * Diablos - The player may attempt to fight and obtain the GF Diablos as an optional GF after using the Magic Lamp.
 * Cerberus - When infiltrating Galbadia Garden, the player may attempt to fight and defeat Cerberus to obtain him as an optional GF.
 * Doomtrain
 * Brothers
 * PuPu
 * Omega Weapon - At the end of the game, the player may attempt to summon and defeat the superboss Omega Weapon.

Final Fantasy IX

 * Morrid's Coffee
 * Hades - At the end of the game, in the water room in Memoria, the player may attempt to fight and defeat the superboss Hades, which in turn allows the player the best Synthesis Shop in the game.
 * Chocobo's Air Garden - The player, after getting the Gold Chocobo, may attempt to challenge and defeat the superboss Ozma.
 * Chocograph - The player may attempt this sidequest by digging up Chocographs in the various Chocobo Forests, as well as Chocobo's Lagoon, and searching out the various treasures in the world, as well as opening up the entrance to Mognet Central.
 * Mognet Central - The player may attempt to give all letters to each specific Moogle in the world for a key item.
 * Tantarian - During the escape from Alexandria Castle, or during the start of Disc 3, the player may go to the Library to challenge and defeat the optional boss Tantarian.
 * Treno Auction House
 * Jump Rope
 * Racing
 * Frog Catching
 * Blackjack
 * Tetra Master

Final Fantasy X

 * Learning Al Bhed - The player has the option to collect all 26 Al Bhed Primer volumes scattered throughout Spira, translating the Al Bhed dialogue to the game's language setting.
 * Belgemine's Aeons - Belgemine the Summoner can be encountered on the party's journey, and the player has the option to pit their Aeons against hers.
 * Collecting Jecht Spheres
 * Omega Ruins - After the player uncovers this area through the Fahrenheit, the player may attempt and defeat the optional bosses Ultima Weapon and Omega Weapon.
 * Dark Aeons and Penance - Only available in the International version. The player must have defeated all of the Dark Aeons and head to the Calm Lands to challenge Penance, the new superboss.
 * Monster Arena
 * Celestial Weapons
 * Remiem Temple and the Magus Sisters
 * Cavern of the Stolen Fayth and Yojimbo
 * Baaj Temple and Anima
 * Blitzball

Final Fantasy X-2

 * Cactuar Hollow - The player may attempt to find all of the missing Cactuars, then attempt to go through Cactuar Hollow to challenge and defeat Jumbo Cactuar.
 * Coliseum (International only)
 * Several Missions are sidequests and not required to complete the game.
 * Via Infinito

Final Fantasy XI
There are many sidequests, some specific to jobs (e.g. Artifact Quests) with others providing a certain spell or other reward. Unlike missions, most quests are standalone and only some form a series. Final Fantasy XI divides quests into nine categories:


 * San d'Oria - quests in the Kingdom of San d'Oria
 * Bastok - quests in the Republic of Bastok
 * Windurst - quests in the Federation of Windurst
 * Jeuno - quests in the Grand Duchy of Jeuno
 * Other - quests in remote areas such as Mhaura, Selbina, and most Chains of Promathia areas
 * Outland - quests in the Outlands areas (Rise of the Zilart)
 * Aht Urhgan - quests in the Empire of Aht Urhgan and elsewhere in the Near East (Treasures of Aht Urhgan)
 * Crystal War - quests during the Shadowreign era (Wings of the Goddess)
 * Abyssea - quests in the new Abyssea add-on packs

Final Fantasy XII

 * Hunts - Besides the first, which is mandatory, the player may choose to accept bills for and defeat stronger-than-normal enemies, the doing of which usually yields extra gil, rare loot, and superior items and weapons.
 * Rare Game - After reaching Archades, the player can return to Phon Coast and talk to a group of hunter Bangaa to join their hunt club for rare game. Delivering trophies to the Bangaa allows the player to purchase rare equipment from their shop, and also the hunt club owner in Archades gives the party some zodiac stones the more rare game the player defeats.
 * The optional Espers Adrammelech, Exodus, Zeromus, Zalera, Chaos, Ultima, Zodiark, as well as the superbosses Hell Wyrm, Yiazmat and Omega Mark XII.
 * Earth Tyrant - The player can help a researcher find out the mystery behind the sandstorms.
 * Ktjn is a Viera in Rabanastre the player can help to decide what to do with her life for various rewards.
 * Viera Matchmaking - The player can help a lone Viera find her love for a reward.
 * Great Cockatrice Escape Sidequest - The player can find the Cockatrices that have left their home in Giza to venture Ivalice.
 * Bhujerban Madhu - The player can find rare alcohol drinks and sell them for gil.
 * Chop Collecting - The player can collect chops by matching people with problems.
 * Footrace Game - The player can race Rikken and his friends at Port at Balfonheim.

Final Fantasy XII: Revenant Wings

 * There are several missions that are not required to complete the game. Most of them are to collect extra summon Espers such as Leviathan.

Final Fantasy XIII

 * Missions - When the player reaches Gran Pulse in Chapter 11, Missions are available that operate much like Hunts. Certain points are spread out on the field used to accept missions, and how well you do on them is denoted by a rank.

Final Fantasy XIV
Sidequests appear to be handled by the Guildleves system.

Final Fantasy Tactics

 * Tynar Rogue - The player must keep Mustadio, Agrias, Ladd, Alicia and Lavian in their party and land in a non-castle city in Agrias's birthday to get the accessory. Available only in the remake for PSP.
 * Balthier - After defeating Meliadoul in Chapter 4, the player must check the rumors "Rash of Thefts" and "A Call For Guards", the player must go to Dorter, after winning the battle, the player can recruit Balthier in their party. Available only in the  remake for PSP.
 * Beowulf and Reis - In Chapter 4, after doing certain errands and checking certain rumors, the player will receive Beowulf as a ally in the Mining Town of Gollund and save Reis and make her and Beowulf permanent units.
 * After completing chapter 3, go to Port City of Warjilis. There will be a cutscene and Midlight's Deep will be unlocked on the map leading to a new island. Midlight's Deep does consist of the best equipment in the game, but also contains the toughest creatures also. Midlight's Deep consists of 10 levels which get tougher and tougher. After completing the first 9 levels, the tenth level will be the home to a special zodiac stone. The final boss in Midlight's Deep is Elidibus. Elidibus uses this special zodiac stone to transform into a Lucavi. A creature named Byblos helps you fight and later joins your party.

Final Fantasy Tactics Advance

 * Shara - The player must complete "A Maiden's Cry", a dispatch mission. After the mission is completed, the player must head to the Pub to talk with Shara, the maiden that was screaming. It was shown that Shara, who has a fear of bugs, cried because of an antlion larvae.
 * Moogle Bride - It involves Montblanc receiving a love letter from Mogumi, a townsgirl. This "Mogumi" asked Montblanc to come to Materiwood. But after the clan arrives at Materiwood, it was actually a trick set up by Reaker, the leader of Clan Rose.

Final Fantasy Tactics A2: Grimoire of the Rift

 * Montblanc - The player must recruit him by completing mission "Wanted: Friends, Kupo!". This mission is unlocked after the player obtains certain Scions which are the Gigas Pendant, Earrings of the Dead, and Pin of Order. Those Scions are what Montblanc was looking for.
 * A Bride for Montblanc is the sidequest of "Wanted: Friends, Kupo!". It is similar with Tactics Advance's "Moogle Bride", but with a different petitioner named "Cois".
 * Brightmoon Tor