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Life aboard Deep Space 9

On DS9 she found there was no need for a botanist, so with the permission of Benjamin Sisko, she opened a school for the children living on the station.

(DS9: "A Man Alone")

Within a few weeks of opening her classroom, she took her eleven students on a field trip to Bajor to visit the grain processing center in Lasuma.

(DS9: "Dramatis Personae")

Later that year, the school became embroiled in a dispute with the Bajorans. They believed that Keiko was teaching her Bajoran pupils that the Prophets were only "wormhole aliens". Keiko argued that it was her duty to expose students to knowledge and refused to teach about the Prophets. The school was then destroyed by a bomb; fortunately, no one was in the school at the time. Commander Sisko held Vedek Winn responsible for the bombing.

(DS9: "In the Hands of the Prophets")

Keiko eventually closed the school down because the remaining Bajoran children left

(DS9: "The House of Quark")

In early 2370, when Bajor was on the verge of revolution, Keiko and Molly were evacuated to the Korat system.

(DS9: "The Siege")

Miles had been reported killed in an explosion while destroying biogenic weapons for two alien races. Keiko viewed the tape of the incident and was convinced that the tape was a fake.This caused Sisko to investigate and find out that Miles was alive.
(DS9: "Armageddon Game")

Miles was replaced by a replica during arrangements for a peace conference. He had been captured by rebels on Parada and his duplicate was programmed to assassinate one of the delegates. Keiko knew about the switch but had to pretend that she did not so the duplicate would lead them to the real O'Brien.

(DS9: "Whispers")

On vacation Keiko and Miles were captured by the Cardassians, and Miles was put on trial for aiding the Maquis.

(DS9: "Tribunal")

In 2371, Keiko joined an agrobiology expedition on Bajor, where she served as chief botanist. It was projected to be a six-month expedition and its first study region was the Janitza Mountains.

(DS9: "The House of Quark", "Civil Defense", "Fascination")

While Keiko was on Bajor, Miles began to focus more on his hobbies to allow time to pass quicker, including playing more racquetball and picking up the game of darts.

(DS9: "Prophet Motive")

In early 2372, Keiko and Miles got into an argument because Miles set up a workshop in their bedroom. Keiko saw this as Miles trying to "live like a bachelor again", and that he was living a "subconscious desire" to push her out of their quarters.

(DS9: "Hippocratic Oath")

In 2372, Miles was arrested by the Argrathi on charges of espionage and subjected his mind to altering that implanted twenty years of prison into his synapthic pathways. Keiko had a very difficult time in trying to make him comfortable and readjust to a normal life.

(DS9: "Hard Time")

Keiko ended her work on Bajor in 2372 and returned to Deep Space 9, after becoming pregnant with the O'Briens' second child.

(DS9: "Accession", "Body Parts")

The child, Kirayoshi, was born in 2373.

(DS9: "The Begotten")

Keiko's body was taken over by a Pah-wraith who threatened to kill her if O'Brien did not help it destroy the wormhole. The Pah-wraith forced O'Brien to convert the station into a gigantic chroniton emitter. Once in position near the wormhole, Miles activated the emitters on the station, but targeted the runabout instead of the wormhole, instantly killing the Pah-wraith inhabiting Keiko's body.

(DS9: "The Assignment")

In mid-2373, Keiko and Molly visited her parents on Earth for an extended period of time. (DS9: "The Darkness and the Light")

When war with the Dominion was almost a certainty by the end of the year, Keiko and her children semi-permanently left the station to live on Earth through the Dominion War.

(DS9: "Call to Arms", "Change of Heart")

They returned by the end of 2374.

(DS9: "Time's Orphan")

The family remained together aboard DS9 throughout the remainder of the war.

(DS9: "Chrysalis")

Keiko made up some crab rolls for Dr. Bashir as he worked to find the cure for Odo's morphogenic virus. (DS9: "Tacking Into the Wind")

Keiko left Deep Space 9 to live permanently on Earth when Miles took a job teaching at Starfleet Academy in later 2375.

(DS9: "What You Leave Behind")