“Just as I'm unable to see a virus without a microscope, it seems I haven't been able to see people for who they are.”
Kimihiko Nikaido (二階堂 公彦, Nikaidō Kimihiko) is the father of Maki Nikaido and a researcher at the Infectious Disease Center of Asia.
Nikaido is presumed to be a widower, left to raise his daughter Maki alone. He homeschools Maki, giving her complicated homework assignments which are later revealed to be part of his research into the virus.
Nikaido regularly gives his daughter injections for her low blood sugar, and has her routinely take her temperature.
In the novel Nikaido's daughter does a good portion of the work at home, cooking dinner, among other things. He loves his daughter, noting that each day she seems to act more and more like her mother.
Nikaido also seems to dislike Kira, stating that the virus being researched could end up causing more deaths than Kira, and later telling the members of Blue Ship that they are no different than Kira.
He first appears in the Infectious Disease Center of Asia. Under orders from Washington, they were to analyze a virus sample taken from Bangnum, Thailand.
After a discussion concerning the effects of the virus, Professor Kujo suggests that the virus is a weapon, saying "Many countries are secretly undertaking the development of virus weapons. Some countries succeed." Professor Nikaido then informs Professor Kujo that the virus weapon has failed, saying, "A virus weapon is a success only if it comes with an antidote. Otherwise, the user will also be infected. I'm sure there was an antidote, but it's of no use now." When asked why, he replies, "This virus has mutated within the last 20 hours."
Nikaido later gives his daughter what is assumed to be the antidote for her to give to Kujo.
Professor Nikaido eventually calls Kujo and tells her to come to the lab. Kujo arranges for Daisuke Matoba, who is a leader of a bio-terrorist group, and his group to come with her. At the lab, Kujo reveals her involvement with the virus, and Matoba explains to Professor Nikaido that what they are doing will benefit the earth's ecosystem, claiming that, "If there are too many, all we are doing is decreasing that number." K finds out that Professor Nikaido has indeed created an antidote already. K and company beg for said antidote, but Professor Nikaido does not give it to them. He decides to incinerate the antidote and delete the data for the antidote. He finally commits suicide by injecting himself with the virus, much to Kujo's dismay, as she tries to convince him that people like himself will be needed in the New World. Kujo shortens Nikaido's suffering by shocking him to death so that he wouldn't have to die from the painful effects of the virus.
Later on, it is discovered that Maki's homework had a hidden message in it left from her father concerning an antidote for the virus, which ultimately helps Koichi Matsudo to successfully create an antidote.
Nikaido is first seen in his lab with Kimiko Kujo, the two researching a virus as per the request of multiple organizations. Nikaido is rather resentful of his work, feeling that his research will merely end up being used to create a weapon of mass destruction.tells her that he has completed an antidote and locked it away. After receiving this information, Kujo hacks into the research facility's system and informs Blue Ship of Nikaido's discovery. The members break into the building, drugging a security guard in order to get in.
The intruders threaten to kill Nikaido, and when he doesn't budge, Hatsune Misawa happily brings in his daughter, having expected that he would say as much. Fearing for his daughter's life, Nikaido agrees to their demands, but at the last minute changes his mind, attacking one of the members of Blue Ship and getting shot in the process, dying soon after.