Kahoku can be found in the Citadel Tower, frustrated at being unable to secure an audience with the Council. He is attempting to gain help in discovering the fate of a group of his marines, who vanished while on a recon mission in the Artemis Tau cluster. The marines were tasked with finding the ship of Armistan Banes.
Commander Shepard can speak to Kahoku after becoming a Spectre, hearing his name from Captain Anderson, while investigating Dr. Chloe Michel's blackmail, or after finding Kahoku's marines on Edolus, reporting that the marines were lured to a thresher maw nest. Once told what became of the marines, Kahoku leaves, vowing to uncover the truth behind the deaths of his men.
As Shepard later learns, Kahoku then contacts the Shadow Broker and purchases information that lead him to Cerberus, in exchange for agreeing to pass on any information that he finds to a Shadow Broker's agent. Kahoku manages to pass on the coordinates of Cerberus' facilities to Shepard, though Cerberus is already hunting him.
If Shepard's squad raids the research facilities on Binthu, they find Kahoku's body, covered with needle marks, imprisoned with some of Cerberus' test subjects. They can avenge him by launching an assault on the Cerberus base on Nepheron. After the assault, one of the Shadow Broker's agents hails Shepard the next time the Normandy's Galaxy Map is accessed, asking for intelligence gathered in the affair. Shepard can then either give up the data, or keep it.
Later, Shepard can hear a news report in the Citadel elevators about Kahoku's death. Due to the circumstances, the Alliance attributes his death to 'natural causes'. The report mentions Kahoku was married and had three children.
Mass Effect 2
Depending on how Shepard handled another assignment, the Commander can hear a news report two years later about Cerberus now being suspected in his death.