It's just a particular style of Japanese boy's school uniform with an arm band, what's the deal? Why we gotta call it 'nazi'?
It's a similar style from Miyamura and Shindou's middle school. It's also the most common one that shows up when I search for 'Japanese boy school uniform' on DuckDuckGo.
Also, for reference, the armband is green, according to the Missing Pieces supplementary season of the anime. So it's not even red like you folks are clearly thinking.
Why you all gotta taint shit like this.