Sear is the older brother of Killian, their parents were killed when they were younger and Sear took it upon himself to raise Killian. Sear never told him how his parents died by being murdered by humans. When Killian found out he hated his brother for not telling him but Sear only wanted to protect him. After the nuclear test held by the humans in the ocean just on top of a Blue city which was completely decimated by the attack, Sear started his own group to make the humans pay for their act. It was never violent, and never involved killing. But Killian disagreed with his ways and took over the group, Sear decided to leave.
The group became increasingly ruthless, killing humans at every mission. Sear could not allow this and contacted Cannon Hawke which in return contacted the council. They devised a plan to stop Killian by asking Killian's former girlfriend Anya to rejoin his team and spy for them. She did and they managed to catch him in the act, Killian managed to escape but his ship was blown up and he seemingly died. When they could retrieve no body, Sear knew his brother was still alive and knew where he was, the island where his parents were murdered. He confronted Killian there on his own, after a brutal battle with his brother he was ultimately defeated, he tried to talk sense into his brother but it was no use, he was too blinded by rage and killed Sear.
Sear has the same powers as any Blue. He can live both under as above the water. He can turn his body into water and use it to attack others, he can shoot powerful waterblasts from his hands. He has also shown great healing powers, as shown when was attack by someone with a fish hook and ripped his entire chest and stomach open, he healed from this in a matter of seconds.