In the future, water has covered much of the Earth due to the effects of global warming. The orphaned Maia Mizuki, 15, just graduated from middle school and has already applied for employment in the elite paramilitary Ocean Agency, part of the futuristic world government. Only the best, most intelligent, and physically fit students are eligible for admission. Maia, the series' protagonist, is set to become one of the few.
But her ideal life quickly falls apart. To her disappointment, Maia unexpectedly fails her entrance exams. Making matters worse, she promptly gets evicted from her house, pick pocketed, taken hostage, then shot. She is "saved" by two women (Rena and Shizuka) that are part of an unorthodox help-for-hire organization called Nereids (inspired by the Greek mythological Nereids ). With nowhere to go, Maia joins up with Nereids, taking jobs from capturing wanted criminals to chasing stray cats, often with unexpected results. Gloria and Yu later join up with Nereids.
"Daphne" in the title refers to a subplot that starts midway into the series and eventually become important to Maia. "Brilliant Blue" refers to the fact that this is a world covered by water with almost no land. The world consists of vast oceans, a few islands, and floating cities.
(Source: Wikipedia)
Maia gets rejected by the Ocean Agency, gets chased out of her house, can’t find a job that offers room and board, gets her wallet stolen and gets taken hostage by a bad guy and then shot.
Maia is involved in a detainee exchange that goes bad. The housing agency confiscates all her belongs. She joins Nereids the all-around service provider.
Maia gets introduced to a martial arts expert, Yu Park. Rena and detective Yagi get taken hostage on a cruise ship. Yu gets reinstated as a Nereids agent after serving 90 days in jail and saving detective Yagi.
Maia gets partnered with Gloria and Yu and discovers the tense relationship they have. Car thieves kidnapped Maia as Yu and Gloria chases a suspect truck.
The girls go to Siberia City where slave traders kidnap Shizuka. Maia has no recollection of being in Siberia before but knows the fastest way to intercept the fleeing kidnappers.
When Maia passed a Loral Tree it sparks an odd feeling. Maia tells the girls about her past. The gang spends an extra day in Siberia looking for clues about Maia’s past.
The 100-year anniversary of the underwater cities raising to the surface is celebrated. The 100-year memorial service for the city of Elpida is also held. Maia, Tsukasa and Millie have a race to show off the Ocean Agency's new hovercraft.
Wong, Chang and Lee along with their rescuer, Mai, seek revenge on Nereids for putting the three brothers in prison. Nereids confiscates the submarine Mai stole.
The submarine is costing a fortune just sitting around. The crew goes out looking for work and Maia finds them a job. The job will be used as a training mission. Maia and an old man go looking for a sea monster. The Yomogi-1 is disguised as a sea monster.
A grade-school boy runs away from home and Maia is sent to Siberia to find him. The branch manager in that city is holding a grudge against Rena. A mechanic is paid off to sabotage the private jet of a wealthy CEO then murdered. Terrorists take over the wave negation towers in Kamchatka.
Maia and the boy are caught in the plot to kill a wealthy CEO. Rena and Shizuka track down the people behind the plot. Maia must pilot and land an aircraft carrying 1000 passengers in the confines of a very large water holding facility.
Mai, Wong, Chang and Lee steal the Agnus, the name they gave the submarine, back. Maia gets taken hostage in an attempt to stop them. Plans for a less than lethal recovery by Nereids goes awry. Maia rescues the treasure hunters from a potentially watery grave.
The stress of almost certain death in her rescue of the treasure hunters triggered Maia to remember an event from her past. She goes to Siberia to look for the time capsule she and her big brother buried under a Loral Tree.
