Played by: Rosalind Chao
Full name: Keiko Ishikawa O'Brien
Species: Human (Japanese descent)
Position/occupation: Botanist (civilian)
Birthplace or childhood home: Earth (Japan)
Parents: Hiro (father); mother (100 years old and living in Kumomoto, Japan, in 2369)
Spouse: Miles O'Brien
Children: Molly (daughter); Kirayoshi (son)
Other family: grandmother
Friends elsewhere: Data and the crew of the Enterprise
Keiko, a botanist and civilian member of the Enterprise-D's science department, married Miles O'Brien in that ship's Ten Forward Lounge. She later gave up her career to move with her husband to DS9.
In "A Man Alone", Keiko at first felt useless because there was no particular call on DS9 for her specialty, but then she noticed that the children on the station had no structured activity, and decided to start a school. She did so, with Sisko's full support, and for the first two seasons was a teacher. When Vedek Winn criticized her curriculum for teaching "blasphemous" scientific principles about the wormhole, Keiko stood her ground, even when the school was bombed ("In the Hands of the Prophets").
In "Armageddon Game", when Miles and Julian were reported dead, Keiko believed that the security log showing the fatal accident was faked, because it showed Miles drinking coffee in the late afternoon, something she said he never did. It turned out she was right about the tape, but wrong about Miles' coffee habits. Keiko continued to be brave and calm in crises, such as the time that her husband was replaced by a replicant ("Whispers"), and when he was put on trial on Cardassia ("Tribunal").
After the Dominion threat became prominent in people's minds, families began moving away from the station. This led to Keiko closing the school in "The House of Quark". She was depressed for a while until, at Miles' suggestion, she took a position as chief botanist on an expedition to the Janitza Mountains on Bajor. The expedition turned out to take much longer than Miles would have liked, however, although Keiko did return with Molly for the Gratitude Festival in 2371 (in "Fascination"). On that occasion, she and Miles fought, but made up.
Finally, after about a year and a half away, Keiko returned to DS9 for good (in "Accession"), pregnant with a son (the result of a visit that was unmentioned onscreen). In "Body Parts", when Keiko was injured in a runabout accident during a botanical expedition, she was unable to carry the fetus full-term, so Bashir transferred him to Kira's uterus. Keiko and Miles then invited Kira to live with them for the duration. Kira did so, and Keiko was fortunately unaware of the brief attraction between Kira and her husband ("Looking for Par'Mach in All the Wrong Places").
In "The Assignment", after Keiko visited the Bajoran Fire Caves, she returned to the station, possessed by a pah-wraith. The wraith threatened to kill her unless Miles performed certain tasks in secret, the purpose of which was to destroy the Prophets. Miles was finally able to foil the wraith and free his wife.
Kira finally gave birth to Kirayoshi in "The Begotten"; and at the end of that year, Miles sent Keiko and the children away to Earth for their safety, due to the imminent invasion by the Dominion. They stayed away for a year, and returned. To celebrate, the family held a picnic on Golana, during which Molly fell through a time portal and re-emerged as a savage 18-year-old; eventually, Miles and Keiko decided to send her back, and in the process regained their little girl ("Time's Orphan").
Keiko stayed on DS9 for one more year until she and Miles finally moved permanently back to Earth with the children ("What You Leave Behind").
Other facts: Keiko and Miles were introduced by Data, and married by Captain Picard. Keiko had a grandmother whom she helped with brush writing as a child.
Appearances: "A Man Alone", "If Wishes Were Horses", "In the Hands of the Prophets", "The Siege", "Cardassians", "Rivals", "Armageddon Game", "Whispers", "Tribunal", "The House of Quark", "Fascination", "Accession", "Hard Time", "Body Parts", "Looking for Par'Mach in All the Wrong Places", "The Assignment", "The Begotten", "Time's Orphan", "What You Leave Behind"