Let's start with the crystal of water jobs, since they're the third set of jobs. It consists of: dragoon, evoker, dark knight, viking, and bard. I think that one of them existed long before the flood of darkness while some existed the day the flood of darkness came, and I assume that the six of them have the affinity to the crystal of water for some reason. Let us interpret these jobs, shall we?

Jobs

The dragoon could have lived in the kingdom of Saronia, and perhaps was the same one who vanquished the avian lord Garuda in the legend. I think he inspired the soldiers of the Saronia military to become dragoons, and this could explain why the dragon spire was built to house equipment for dragoons. I can imagine him being a caring type of guy, the way that he's willing to save his kingdom from the threat of the avian lord. His cause of death is dying from his wounds after vanquishing Garuda (keep in mind that this is hundreds of years before the game starts), and spent his final moments training the future dragoons in jumping high and land on enemies with spears.

The evoker may have lived in Replito, a village of summoners located at the northern point of the continent where Saronia is located. He was traveling in search of the legendary summon spells, but no luck because catastro is located in the underwater Saronia catacombs. Frustrated that he can't access the location of the catastro spell, he went over to Amur (the town of canals) and stayed there for a week. I can imagine him as being eccentric and a clumsy, since being an evoker his summoning spells work in random and he has a strange way of thinking. His cause of death is when he tried going to the ancient ruins without being prepared, only for boulders of adamantite to crash down on him during an earthquake caused by the flood of darkness.

The viking may originates from Viking Cove on the floating continent, back when it was a part of the surface. Perhaps the reason why his job class wasn't available on either crystals on the floating continent was because he was sailing to explore the world at that time, and he has an affinity to the crystal of water. He had spent his time sailing from Duster to Amur, having forgotten his home. When the flood of darkness began seeping, freezing time on everything it consumes, perhaps he fled to the Temple of Water for safety. But he saw that the continent that he lived on broke off from the world, becoming the floating continent. Angry at himself that he didn't bother coming home when the flood of darkness swept the world, the viking spent his remaining days at the Temple of Water while fending off monsters. I can imagine him as being fierce yet adventurous, willing to explore what the world has to offer. His cause of death is starvation (since he exhausted his food supply waiting for weeks for someone can rescue him) and fighting monsters to the point of exhaustion, he spent his final moments trying to fend off the monsters while starving to death.

The dark knight may have lived in Falgabard, a village of dark knights surrounded by a mountain range. I can assume that he was Ingus' father back then, at least according to an unused dialog about how Ingus remarks that the village feels familiar. I think that the dark knight loved his wife and his unborn son, and when she died giving birth, he became depressed since he had to take care of his newborn son alone. The dark knight was a loving and caring guy until his wife died, even though he loved his son he became suicidal as a result of depression. On that day he left his son under the care of a fellow dark knight, he traveled to the Cave of Shadows (it's a cave full of bones and skeletons of monsters and unknown creatures, and it's where the fang of earth is located) to train. He fought the monsters that are capable of multiplying and dividing, while going deeper into the cave. However, his luck ran out when he used up his potions to restore his health after using souleater ability on the monsters. His cause of death is when the monsters tore his legs, and he spent his final moments crawling back to the beginning part of the Cave. Then he entrusted two of his dark swords and armor to a fellow dark knight, so that might explain why there's treasure chests in the waterfall in the village.

The bard made have lived in Duster, a village of geomancers and bards located on an island south of Saronia. I can imagine that the bard is the sister to the geomancer, since the two had lived in the village. Since her sister went to the continent to train, the bard traveled around practicing her singing skills on her harp. I can imagine her as an optimistic and focused type of girl, much like her sister. However, when the flood of darkness began sweeping through the world, she had fled to the Cave of Tides because she was nearby on her travels at that time. Once she ventured deep into the cave, it was too late to go back since the exit is sealed off by the maidens of water to prevent the darkness from overtaking the crystal of water. I can assume she uses her songs to confuse the monsters and flee into the bottom of the cave, and then she encountered the crystal of water that had told her that she was destined to lend her aid to the warriors of light along with the others of different jobs. Her cause of death was drowning, because it will take a long time for the warriors of light to get to the crystal of water and there's no food to eat.

Conclusion

All these jobs have rather tragic ends, but the crystal of water have absorbed their jobs and their spirits in order to bestow its light to the warriors of light and aid them. I can imagine that, after the warriors of light are blessed by the crystals light, the spirits of the jobs meet others of the same situation. The bards spirit is reunited with the spirit of her sister (the geomancer), the dark knights spirit reunites with his son (who is a warrior of light). The viking wanted to go home, even though it's no longer possible due to being dead for decades.