This achievement is story-related and can't be missed.After setting your base at Plumpet Island and knowing about uncle Benjo situation, you'll be tasked to return to the Zabirum Temple.
To get there you'll need to leave Zaber city and head in the Zabirum Temple direction on the free world, maybe facing some enemies on your way.
Upon arriving at the Temple, you'll need to fight your way down until you notice Ive. From this point you'll have a few more fights and will need to enter a cave where a puzzle must be solved. After solving the puzzle, you'll meet Ive and the achievement should unlock when conversation with her is over.
For a specific puzzle guide, check the amazing Earthlock walkthrough here on TA:
Earthlock Walkthrough