She was originally one of the first heirs born along with Orca, and grew up alongside her for a few years. However, when Orca became more desperate for the throne, she fled to the ruins of the Summer Place for a year in fear because she wasn't sure if Orca would see her as a threat. However, when the next royal animus test came along with Anemone, she reemerged seeing as Coral was still alive. She was greeted with great delight, and came back to the Summer Palace. She learned of Orca's death, and while she was upset, she was also received to know that her life wasn't in danger.
After that, she knew Orca's fatal flaw-she was too young. So she waited, training in secret, waiting for the day to soon come. She hid herself away from Coral's other daughters, as Anemone was an animus and was thus a huge threat, as an animus could be nice one moment, then strike the next.
Now seven years have passed since Orca's death, and Seaviper is close to being ready to take on the throne. She's gained support, visited many places and seen all the tribes, forming bonds with them along the way. However, she still felt nervous. Orca, whom she found out was an animus after Tsunami came and went, even with her powers, she was still defeated by Coral. Nervousness and the desire for power consumed her in the moment, and she consulted the Mirror of Twisted Realities, smashing it and letting Repivaes out.
After that, Repivaes already began changing her. It first began with her memory of letting them out, making her think she's always had the green streaks in her eyes and the emerald animus vessel. She began to constantly use her power and train, unaware that the more she did so, the more she allowed Repaves to take control and the less likely she would be able to take back control.
It finally came to the point where she challenged Coral for the throne. Repivaes was in partial control, and the match didn't last long. Combined with Coral's unwillingness to fight her daughter, and Repivaes desperation for the throne, Coral was close to being killed. However, Seaviper, who was having second thoughts about killing Coral, took control and used her animus powers to disguise Coral as an average SeaWing with fake memories, and in put in place a dummy made to look and act like Coral, and quickly erased the viewing SeaWings' memories about the dummy so they didn't know that the dummy was fake. Repivaes then took back control, and "killed" the dummy Coral. Even when "dead", the dummy still looked like Coral except with a gruesome slash across her throat, and blood leaking out, which fooled Repivaes and the surrounding Seawings into thinking that Coral had actually died.
Since Seaviper had discovered that Repivaes had possessed her, Repivaes took action and "chained" Seaviper's subconscience to the floor, rendering her unable to take back control and leave Repivaes in permanent charge. Repivaes then exposed herself, and ruled under fear from the SeaWings. Any heirs who showed signs of resistance were killed in the most gruesome way possible in public to show that they were the Queen.
At one point, Repivaes tried to kill Auklet, and despite Seaviper's subconscience being "chained" the the floor, she could still hear and see what was going on. With the dragonet's cries and her desire to escape, Seaviper "broke free" from the "chains" and retook control. In her short moment of control, she was able to banish Repivaes back to the mirror, and wipe all the SeaWing's memories about that event, and got the real Coral back also with no memories of the events.
Coral currently is still the queen, and while Seaviper still has the memories of what happened, she keeps quiet and won't be challenging for the throne for quite awhile. However, she still eyes some heirs challengingly, as they still may be a threat to the throne, and she still has a small desire to have it. This is because while Repivaes was banished back to the mirror, the emerald Repivaes used as an animus vessel is still embedded in her forehead, leaving behind traces of Repivaes's personality in Seaviper.