Sayoko Nanamori is Itsuki's research assistant. She is shown to hold unrequited feelings for Itsuki, and to react angrily if anyone touches on the subject. This leads to a small running gag in the series: Whenever she is particularly upset about Itsuki, the windscreen wiper on her car is shown to make an interval swipe on its own.

In the movie, Nanamori appears only in a glimpse. In the manga, Nanamori is a malevolent Mu agent and facilitates Ayato's escape from TERRA.