It’s late but:
Huge infodump:
-Sugimoto is based on two real-life people: The first is a man also named Saichi Sugimoto, with a different kanji spelling (杉本佐一). The real life Sugimoto was in fact the great-grandfather of the series creator, Satoru Noda. He was a soldier of the 27th Regiment of the 7th Division and was celebrated as a war hero. The fictional Sugimoto has only borrowed the name of the real Sugimoto.
The other was a soldier named Hiroshi Funasaka, who had received the title of "Immortal" after having survived many injuries including a shot to the neck and a hand grenade blast
-Shiraishi is based on Yoshie Shiratori who is known for having escaped from prison at least four times.