The Nepto Temple is a water-themed dungeon, and you'll need to remain in Mini form for most of it. The enemies here are often aquatic, so Lightning magic (Thunder, Thundara) will be highly effective. Navigate the temple's winding paths, solving simple puzzles involving switches and water levels. The main objective is to retrieve the Nepto Eye, which has been stolen by the Kraken. The Kraken is the boss of this dungeon.
Boss Strategy: Kraken
The Kraken is a formidable foe, especially in Mini form. It is weak to Lightning. Have your Black Mage repeatedly cast Thunder or Thundara. Your White Mage should focus on healing with Cure spells. Physical attackers will do minimal damage in Mini form, so they should either defend, use items, or if they have any offensive magic, use that. Be prepared for the Kraken's powerful physical attacks. After defeating the Kraken, you'll retrieve the Nepto Eye and can return it to the Nepto Dragon, who will then allow you to pass through its mouth, leading to the next area. This also unlocks the Thief job, which is incredibly useful for its Steal ability and high Agility.