Theory: I think I've found the rpg character Noda is imitating .
As stated in the manga, Noda believes the afterlife world to be a game, an rpg to be exact.
Many characters point out that he seems to be imitating a video game character, I think I've found who.
Felius Arwin from Wild Arms XF: http://wildarms.wikia.com/wiki/Felius_Arwin
Their character designs seem pretty similar, their personalities are quite simalar as well.
Felius uses halberd type weapons just like Noda does.
It was also released three years before Angel Beats, so maybe there's a possibility that Noda's character was based on Felius? Or that Noda is imitating him? It might be far fetched, but I wanted to put it out there as a possibility.