Sea Fantasy

When you have the option to go to Volkeinos or Lanome, pick Volkeinos first. That storyline leads you to a dungeon that provides the ability to teleport short distances via a magic tool. Once you have that magic tool, head to Lanome and teleport past the locked door. A cutscene will play out indicating you weren't supposed to do that and then the achievement will pop.

This is missable because you need to teleport past the door while it's locked. If you do the Lanome quest line first, the door opens up.

Craft the White Gold Rod as soon as you are able to. It increases the chance of reeling in a crown-sized fish by 3%. It's more than sufficient for all the end-game content.