The Aquarius Gemstone
Written by MSG Commander
The door that matches this stone is in Dyad Hollow, which you have not been to before, and which is literally just southeast of Kashinew, surrounded by mountains. (If you end up down by the Earth Shrine, you've gone too far south.)
This dungeon's another long one, but it's nowhere near as complicated as some of the others have been, and the enemies aren't quite as strong either. I still don't recommend putting the random encounters on Auto, but it probably wouldn't kill you if you did. (Unless it's just Sirens, then Auto away.)
Dyad Hollow is essentially split up into two separate paths, both starting from the northwest corner of the first floor.
The Northwest Path
From the sealed door, go to the west and follow the path to an Energi Element in the southwest corner of the room. Then go north, and follow the path to the west set of stairs that lead down to the second floor. Follow the path to the northeast to stairs down to the third floor, and then go south to stairs down to the fourth floor.
On the fourth floor, follow the path all the way to the treasure in the southwest corner of the room. Save your game, and open the chest to get the God Axe.
a Guardian V
I used Aura, Mini Big Bang, Catastrophe, and Meteor Strike. Halfway through the first round, he used Alphadia and killed half my team. (But I still won...)
After the battle, go back to the entrance and follow the Northeast Path to get the rest of the treasure.
The Northeast Path
From the sealed door, go to the north and follow that path all the way around to the east set of stairs leading down to the second floor.
Follow the path to the east and get the Energi Element. Then go north and follow the path around to the west to stairs down to the third floor. Follow this short path to stairs down to the fourth floor.
On the fourth floor, go all the way to the southeast corner of the room to get God Mail.
Once you're done here, go back and talk to the researcher one last time. He tells you your search is over, but then he mentions that historical accounts say there should still be at least two more types of weapons out there... (Although as near as I can tell, that's just random dialogue, and not a clue that there are in fact more Legendary Weapons to be discovered.)
If you've found all the Legendary Weapons, when you leave Dyad Hollow, a mysterious voice calls to you, challenging you to prove your strength. Your challenger is on an island southeast of Nolthia. (Note: you don't have to do this challenge to complete this Quest. In fact, if you attempt the Ultimate Title challenge now, you will most certainly fail. Save it until after you've beat the game, and all your characters are at Level 99.)
- Energi Element - located in the southwest corner of the first floor.
- God Axe - located on the southwest side of the fourth floor.
- Energi Element - located on the east side of the second floor.
- God Mail - located on the southeast side of the fourth floor.