The Arcadia's executive officer and one of her youngest crew members, Kei Yuki is one of the only three women aboard the ship. Due to the shifting backstory of the Harlock series, Kei Yuki's background varies depending on the series.
Kei Yuki is one of the youngest crew members on board the Arcadia. She joined the crew at the age of 16 after Harlock attacked a military prison transport taking her back to earth, after she assaulted a military officer. Harlock offered to let the orphan Yuki join his crew, as she displayed the independent, rebellious spirit demonstrated by Harlock and other members of the Arcadia's crew. At the start of the series Yuki is the executive officer of the Arcadia and watches over the Arcadia's latest (and youngest) crew member, 14-year old Tadeshi Daiba, himself orphaned at the hands of the Mazone.
Kei Yuki, the daughter of the proprietor of a pirate radio station, speaking out against Earth's occupation by the forces of the Illumidas Empire, joins the crew after her parents are executed by occupation forces. Kei becomes a mentor figure to Revi Bentselle, a young girl who ends up staying aboard the Arcadia, while also working to find the Treasure Island of Space, which holds the secret to freeing Earth from hostile forces.
Following Harlock's mysterious disappearance with the Arcadia, Yuki captains her own pirate ship, along with some other members of the Arcadia's crew, including Engineering Officer Yattaran. When Yuki and her crew are captured by forces of the Earth Government, Harlock returns from his mysterious retirement with the Arcadia and Tadeshi Daiba and rescues his former crew. Together again, they set out to save the universe from the predations of the mysterious Noo, a force capable of driving entire armadas insane.