Mass Effect: Foundation Edit
Shortly after his trial for espionage and subsequent release due to technicalities, Keiji visited his and Kasumi's apartment on Illium, initially happening upon a darkened room until he switched on the lights. Kasumi had the apartment decorated with a romantic ambience, and he held out his hands to feel where Kasumi might be hiding. His lover decloaked in front of him, and after the welcoming kiss they discussed Keiji's release. Kasumi was bored of Keiji working for the Alliance, so he shared with her the details of their next job: a heist on Bekenstein that Keiji claims would require all their skills to successfully pull off.
The pair encountered more guards than they expected inside the estate, making Keiji wonder if their presence was anticipated. Kasumi split from him to reconnoiter further in, relaying her findings and observations by comms. She took out some guards to distract them from Keiji, who made his way to the end of a hall in the third floor. He was in the middle of praising her when his comms cut out: the estate's owner, Donovan Hock, stabbed him in the head.
Hock forcibly extracted Keiji's graybox and left, leaving Keiji to bleed out on the floor. He managed to stay alive long enough for Kasumi to reach him. The graybox contained all that's left of his love for her, and Keiji told her to get it back. His last words were of love and directing her to survive, and his body was left behind as Kasumi cloaked and vowed to find him again.
Prior to his death, Keiji also stole a decoy program that Kasumi put to good use during their ill-fated run at Donovan Hock's property.
Mass Effect 2 Edit
Keiji Okuda was Kasumi Goto's former partner, lover, and a former member of the Alliance Intelligence Agency under the alias of Abraham Rumoi. They first met when they were hired to steal the same painting. Instead of turning it in to their employers, they kept it. Due to his work he had a graybox implanted to allow him to remember what he needed to in order to do his job.
Eventually, he acquired some very sensitive information that if made public would do a lot of damage to the Alliance's reputation. When he acquired the information he came under prosecution due to his work of stealing classified information and selling it. However, prosecuting attorneys were forbidden to use his graybox memories to incriminate him due to an Alliance statute based on the Fifth Amendment of the U.S. Constitution about self-incrimination. After the trial, he vanished and was eventually tracked down and killed by Donovan Hock. Hock removed his graybox and has been trying ever since to crack it.
After Kasumi joins up with Commander Shepard, she asks him to help her retrieve the box during a mission to Hock's estate on Bekenstein. The mission eventually sees to the killing of Hock and the recovery of Keiji's graybox.
After the mission, Kasumi accesses the box and sees her partner one last time. The hologram of Keiji says that if she is watching the recording then he is dead. He reveals the data, saying that it would impact the Alliance's reputation if it ever got out. He begs her to destroy the data and the memories. Shepard can persuade Kasumi to follow Keiji's wishes or keep the data.
Mass Effect 3 EditReaper invasion, Shepard finally learns what data Keiji Okuda was so desperate to keep hidden: previously, the Alliance conducted a black ops raid on a batarian group that was studying Reaper technology. Keiji was aware that if this information was released, the batarians would likely go to war with the Alliance.
During the battle for Earth, if Shepard activates the Crucible and chooses to merge organic and synthetic life, and if the graybox was saved, an apparition of Keiji can be seen in the aftermath reunited with Kasumi.