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"I'm not going anywhere until I know all those things are dead."
― J. Katayama to the Marine  [src]

J. Katayama is a minor character in Doom 3. He was a maintenance worker assigned to the Caverns area who managed to survive a huge chunk from the demonic invasion, thus being the final survivor the player encounters.

The player will find Katayama hiding under the thermal regulation pumps from the demons. He questions on the player's arrival, asking them to leave for fear that they can attract the demons to his hiding location. He then asks the player to take his keycard, which will allow them to gain entry further into the Caverns. If the player persists in speaking to him, he will refuse to leave and asks the player to seek for help.

His fate is unknown, but the intro of Resurrection of Evil states that only one survivor (the player) was found, suggesting he eventually succumbed to the invasion. On the other hand, given that he had survived long enough shortly before the player seals off the final portal to Hell, he may have persisted further by continuing to stay at his hiding spot before the Fleet found him.