Tide-Line Blue is set after an environmental disaster later called the "Hammer of Eden" has submerged 90% of the Earth under water and taken six billion lives. The series begins fourteen years after that event with the new and remaining countries being brought together under the New United Nations. However, Gould, a renegade submarine captain wishes to use military force to create peace in the new world order, while Aoi, the secretary-general of the New UN, wishes to use diplomacy, and a boy named Keel finds himself caught up in the middle of it all.
A carefree 14-year-old boy living in the city of Yabitsu. He was orphaned at an early age and was taken in by New United Nations Secretary-General Aoi. He has feelings for Isla, but is unable to express them to her. Despite his happy-go-lucky attitude, he took care of Isle in the aftermath of the attack on Yabitsu and ended up boarding the Ulysses in order to obtain treatment for Isla.
A 14-year-old boy and twin brother of Keel, who serves as a lieutenant on the Ulysses. He was brought up as a soldier after Gould rescued him as a child. He was chosen to convey Gould's declaration of war to the new UN. The twins were temporarily reunited in the confusion after the attack, when Tean delivered Isla's baby. He advised Keel to leave Yabitsu and gave him an insignia to identify him should he wish to leave Yabitsu on the Ulysses. He was captured by new UN forces before he could return to the Ulysses.
A 16-year-old jewelry crafter who makes her living by selling her handmade silver trinkets to sailors who stop in Yabitsu. She is single mother who became pregnant at a young age. A strong and lively girl, she doesn't let the situation get her down, no matter how bad it may seem. She becomes a very popular person on board the Ulysses in part because she is always willing to undertake any chores that need doing.
New UN Secretary-General and Keel's adoptive mother. She is an excellent politician and administrator but does not know how to deal with her teenaged son. She is trying to reestablish a world government for the benefit of everyone in the aftermath of the "Hammer of Eden" but is hampered by power struggles between the prospective members.
Captain Gould (グールド, Gūrudo)
Voiced by: Takaya Hashi (Japanese); Steve Olson (English)
A captain in the former U.S. Navy, he is the commander the Ulysses, a strategic nuclear submarine. He was seriously injured and received burns to the right half of his face in an attack at a peace ceremony between the new UN and a previously hostile nation. He hated the war and agreed with the ideals set forth in the peace accord but was disillusioned when he lost all of his men in the attack on the signing ceremony. He now considers peace by diplomacy a lost cause and is determined to bring peace to the world in a different way - through his overwhelming military might. To that end he has broken away from Aoi and the new UN and has declared war against the rest of the world.
A deputy officer on the Ulysses. She is a quiet and beautiful 19-year-old woman, with a firm belief in Gould. She excels at being a soldier and Keel becomes flustered in her presence.
Captain of the Teshio, a Maritime Self-Defense Force Aegis destroyer and new UN flagship. He, along with Aoi and Gould, was confident that the establishment of the new United Nations would benefit mankind. Gould's actions have caused a severe strain on Satoyama's relationship with him.
Blantyre "Blanc" (ブランタイル, Burantairu)
Voiced by: Junpei Morita (Japanese); Paul Huson (English)
The captain of the Electra, a beached nuclear-powered aircraft carrier that was the main base of operations for the establishment of new UN and Yabitsu town. The ship and town were destroyed when the Ulysses attacked.
President of the Republic of Wei, which is opposed to the philosophy of the new United Nations. He and the country place their interests before those of the General Assembly.
King (キング, Kingu)
Voiced by: Naomi Kusumi (Japanese); Tommy James (English)
An American oil tycoon and partner in Aoi's plans.
Captain of a floating dock who makes a living by repairing ships. Although he has a rugged exterior, he is an honest person who always keeps his promises. He undertake the repairs to the Ulysses and loses wagers when gambling with Keel.
Tean and Keel's father. He was stationed at Space Station "Freedom", with his wife and children, to map the rapidly changing terrain. The family escaped to Earth and he stayed behind on the station.
Depictions of technology
This series is known for being relatively realistic in its use of technology and the technical accuracy of its animation.
Teshio: A 160-meter, 5050-ton Aegis-equipped escort ship, formerly of the Japan Maritime Self-Defense Force and now the New UN's flagship. Uses the ASROC anti-submarine missile system, an anti-ship missile called SSM-1B, a missile called SM-3, and surface-to-air missiles (SAM). It also has a helicopter deck.
Han: A nuclear attack submarine from the country of Gui (formerly China) that has a stealth propulsion mode, and unguided supercavitation torpedoes. It is 11,050-tons, 120 m length, 25.3 m width, and 21.2 m in height.
Freedom: A crewed space station orbiting Earth. Originally a private venture, it was intended to search for coal deposits. After the Hammer of Eden it was used to map the new surface of the Earth, as well as underwater terrain and new ocean currents.
