Tomiko was a research scientist for the Weyland-Yutani Corporation working on LV-1201. She debuts in the Marine level "Betrayal" and bribes Corporal Harrison into giving her a disc that she needs for information on her brother. She later helps Harrison and gives insightful tips. In the final Marine level "Savior", she sacrifices herself and blows up the FOP (Forward Operating Pods) in order to get rid of the events that happened on LV-1201.
She may have had a small affection for Harrison in the later levels.