Had to play 3 times to understand how this one works, basically you need to do all the achievements in 1 playthrough.
Since you start the story you need to do, in 1 single play:
(Unmissable)
- Defeat Melira in all the 4 levels.
- Get Runestone.
- Get all Runestone skills.
(Almost unmissable)
- Reach the maximum speed surfing.
- Upgrade Galand's power for the first time.
(Missable)
- Open 20 Experience Chests.
- Complete the Harmony Obelisks area.
- Complete the Fire Hammer Coliseum area.
- Complete the Quick Imp area.
- Complete the Quiet Rock area.
- Complete the Fisher Fish area.
- Find all relics in the Temple of the Elder Protectors.
- Find all relics in Windmills Town.
- Find all relics in Woodborn.
- Find all relics in The Vineyards.
("Easy" to miss)
- Upgrade Galand’s power 6 times.
- Find all relics in the Red Plains of Oblena.

If you do all this in a single playthrough you get that last achievement.

I missed 1 in the first playthrough and had to play it all again.
I completed that 1 that missed in the 2 playthrough and had all achievements except the "Effie, a fantasy adventure".
In the 3 playthrough i did all this and got the achievement, so this is it, good luck achievement hunters :)