There are several people who either come into contact with or indirectly affect the main characters of the story.
Kasahara Yuuji. He too meets Cell Four at the JSDF garrison. A loyal friend, he is traveling with Shinpei to find a doctor for his infected son. Kasahara believess there is no hope or cure for the child, but follows his friend anyway.
Dr. Yukko Sakagawa. This doctor contacts the Shouran Academy from her lab on the Sea Firefly. She asks the boys bring her a newly infected F-virus carrier so she can create a radical cure for the M-virus.