Zalera is located in the newly opened areas of the Barheim Passage and you can challenge the Esper anytime after you have reached the Ozmone Plain.
In order to regain entry into the Barheim Passage, you must obtain the Barheim Key by completing the Desert Patient side quest. Click on the link below for more information:
Warp to the Dalmasca Estersand orange Save Crystal which will land you in the South Bank Village. Head south away from the South Bank Village towards the Murmuring Defile and use the Barheim Key to gain entry.
Enter the Barheim Passage and follow the Zeviah Subterrane area north into the Great Central Passage. Turn left (west) and follow the pathway to the East-West Bypass and then south down the Zeviah Span.
Knock the “Precarious Cart” over to open up the pathway if you have not done so previously and continue south down into the West Annex.
The pathway leads right past the area where you may have already fought Bloodwing as part of Hunt 16: The Deserter’s Revenge. Follow the pathway west until you reach Terminus No. 7 Adjunct which has a Save Crystal that you can use to heal up and save your game. Heading west into the next area (Terminus No. 7) will initiate the fight against Zalera.
Level: 63
HP: 258,001
Steal: 
Virgo Gem (55%), 
Hi-Ether (10%), High Arcana (3%)
Steal (IZJS Version): Virgo Gem (55%), 
Elixir (10%), High Arcana (3%)
The battle against Zalera is very non-traditional. Zalera does not have many attacks but will instead focus on status affects, instant KO attacks and relying on Dead Bones allies that it summons in order to defeat you. You will also only have 5:00 minutes to defeat Zalera or the battle will reset and automatically transport you back out to Terminus No. 7 Adjunct.
First and foremost, you should make sure that your party members cannot be killed by a move called Prime Lv. Death. This will kill any of your party members whose level is a prime number; i.e. they should not be any of the following levels:
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97
You should consider returning back out into the West Annex and leveling up any of your party members if they happen to fall on any of the prime numbers listed above.
Remove any of your weapons if they have an elemental affinity as Zalera will resist all elements. Some of the status effects that it will cast include Sleep and Stop, so equip your characters with a 
Nishijin Belt if you have it and make sure that one character has a Black Belt equipped to prevent Disable; having all of your characters impacted by the Disable status affect at the same time will result in an instant Game Over.
Zalera will raise its Defense and Magick Defense stats whenever there are Dead Bones enemies still alive – focus on killing them first. Setup Gambits on all of your characters to cast 
Esuna on other Allies to get rid of Blind/Sleep/Disable as quickly as possible.
Zalera will start casting a spell called Kill when its HP gets low which means that some party members are going to be killed. Setup a Gambit to use Raise or a 
Phoenix Down as well on all of your party members so that they can get back up and running as quickly as possible. Because your party members are going to be killed often, you may want to remove some of your buff Gambits later on in the fight, as your party members will waste a lot of time re-casting Protect / Shell / Faith / Bravery / 
Decoy / etc. every time a party member dies.
A video of the battle in the original version is included below:
A video of the battle in the Zodiac Age version is included below:
Congratulations – you now have Zalera as an Esper which you can use in battle!
Note: If you will be continuing on to the next optional Esper battle, continue westward to exit Terminus No. 7 where you fought Zalera for a shortcut back into the Garamsythe Waterway.
Zalera can be summoned during a fight. It will use Kill to cause instant death on a target enemy (unless they are immune, which most bosses and powerful enemies are). It can also use a move called Condemnation, its ultimate attack, which will instantly kill any enemy with less than 9,999 HP (max).
Unlocking Zalera on the License Boards of certain jobs will unlock additional License Boards:
Steal, Poach
Blood Sword, KarkataTravelerTravelerThere isn’t really an optimal class to have pick up the Zalera License. Giving your Black Mage Steal and Poach has limited applications, your Bushi likely won’t use the two Swords, the Traveler Technick is of minimal use, HP has limited value in end-game content and Ether Lore 3 is useless. Take your pick!
