In the back of my mind i think they're the same person-
Nagisa Shiota, primary school age : Forced to study rigorous abusive hours as a child
Nagisa Shingestu High school age: A flunk out in the flunk out class
Nagisa Shingetsu is actually based off of Nagisa Shiota! design wise, at least, but I do think content/personality traits insproration was also there ^v^