If you finished the game already, I recommend taking the Moka shortcut in the main menu, as it's the route I know you will not have any issues with backtracking for any bubbles.

Also! The pictures in this guide may look slightly off, because they were mostly taken before the map redesign update, but they are essentially in the same spot, with the exception of #6 that I updated the pic for. (and I updated #4 while I was at it because the new purple kelp forest is so pretty)

First bubble's the easiest, It's in the starting area, near Triche's house. Just walk down the steps coming from the north and you can grab it no problem.

Another very simple one to find, it's in the northeast part of the beach area where you encounter Sinus and Joru.

This one's on the left side of the kelp maze where you rescued Tae. The path isn't super obvious, off of a dead end. It's a very missable one.

This one's just to the left of Tae's home, in the purple kelp forest to the west.

Bubble #5 is located in the right entrance of the Murky Water Cave, through the opening at the beach where you met Sinus and Joru. You can enter it after your second encounter with the duo where you save Joru from the crab.
It's fairly missable since you can only enter the cave late in the game, and it's never actually required in any of the routes to enter the Murky Water Cave through this route, but it's not hard to find if you do go in there.

Very simple one, it's just to the right of Moka's house, available near the end of the game.
As of the map redesign, it's in a similar spot than before, to the right of Moka's house. At the "crossroad" there, just go south and you'll find it at the end of that path.

This one's in the cave at the end of the game, it's pretty easily missable mostly due to the fact you only have a small window of time to grab it before the end of the game.

Right after making the cave collapse with Albica's help, you will want to head all the way to the right, then follow the path south to find it, if you grabbed every other bubble at this point, you should get the Explorer achievement!

Thanks for reading, and for supporting KigyoDev!
Hopefully this guide helps a few people in their journey become Pro Gamers,
(or at least to get the Pro Gamer achievement).

Farewell!