Littlevili's background is currently unknown. She may have some correlation to the item or owner of the key item 'Elda's Cup', which is needed to unlock her. She may also have a connection with the Head Monk, Baldi, who played a role in the quest you unlock the key item from.
To unlock Littlevili you must first complete the following quest:
After completing that quest, the next quest will appear which you must complete to receive Elda's Cup:
Now that you have Elda's Cup in your key items you must complete any quest with it equipped, even so, you will only have a 20% chance of unlocking her. Luckily, you may complete quests until you get her. Be aware that once you complete Caravan Guard, which requires this key item, you will no longer be able to get her on your team.
Apart from her level, Eldena will have stats similar to any other Red Mage. Her level will depend on the average of your current team's level, Eldena's level will be four higher than that.
Eldena will start knowing the following moves, however her character acts like a normal Viera, so she can change jobs and learn new moves:
|Barrier||Grants a single target both Protect and Shell.|
|Doublecast||Allows you to cast two spells in a row on a single turn, however the needed amount of MP for both spells will still be consumed.|