Head to the Bamboo Grove and find the house surrounded by water. Look to the left of the main bridge for bushes and pink flowers, then enter the hidden underwater tunnel and climb the ladder to find NPC Urokodaki. After speaking to him, you start the quest. The goal is to collect five glowing blue sea crystals from the nearby riverbed. Their locations are random, but they’re always close to the surface. Set your spawn at the Bamboo Grove Sanctuary and reset after finding each crystal to make the process much easier. Keep an eye out on your breath meter so you don't drown.
Are you looking to achieve the epic Water Breathing style? Our guide on all Underwater Rocks locations in Slayers 2 takes you one step closer to it. Follow along carefully and let the student become the master!
How to Start the Underwater Rocks Quest in Slayers 2

Upon entering the game, you spawn in the main town area of the map. In order to start the Underwater Rocks Quest in Slayers 2, you must head over to the Bamboo Grove. You can find it's exact location on the map in the top right corner of the screen. Here you will look around for a house situated on what appears to be a small island, surrounded by a body of water, various bridges and waterfalls, making the location fairly easy to recognize once you are nearby. Stand in front of the house and look to the left of the main bridge that leads up to it. You should see bushes next to some pink flowers. This is the area you should investigate. Hidden beneath the foliage is a small underwater tunnel that can be easy to overlook if you are simply running through the area. Enter the tunnel and follow it forward. At the end, you will find a ladder that you need to climb. Don't worry about running out of breath while traveling through the tunnel, it's relatively short, so you should have more than enough time to make it through without drowning.
Once you climb the tunnel you will enter a room where NPC Urokodaki, the Water Breathing Trainer, is located. Interacting with him will provide you with the quest. Now the real challenge begins!
How to Find all the Rocks in the Underwater Rocks Quest in Slayers 2

After you've successfully started the quest by speaking to NPC Urokodaki, leave the tunnel the way you came from, back to the main area in front of the house. Now, your main game objective is to collect five glowing blue rocks, or rather sea crystals, from the riverbed. The locations are not always the same, they are generated randomly. But they're never deep in the water, always close to the surface. Deep enough that you need to dive but not enough for you to drown if you're properly keeping an eye on your oxygen levels. In case you do accidentally drown, don't worry, it only resets your current dive rather than failing the entire breathing style questline.
The easiest way you're going to avoid wasting time is by setting your spawn point to be the Bamboo Grove Sanctuary. You can locate this point in front of the house, simply interact with the only purple crystal on site and set it.

Getting all the sea crystals in one run is very unnecessary. Each time you've located a rock, simply reset and go back to your spawn point. You won't run out of breath and your progress won't be lost.
As said before the crystals will be near the surface. On rock beds or elevated terrain areas. They will be emitting a shimmery blue color, hard to miss even if you are playing the quest at night time.
Are you enjoying Slayers 2? All the different techniques, quests, weapons... So cool! But the game can get hard sometimes huh? In case you get stuck our How to Get Sound Breathing Style in Slayers 2 – Location & Requirements & All Secret Weapons in Slayers 2 & How to Get Them might help!