There is a scene that Mumen Rider’s student days from One Punch Man VOL.1. It shows one of Japanese school culture difference in terms of commute between urban and rural area. Let me introduce it in this article.
Helmet is mandatory for school commute by bicycle
Quote One Punch Man Volume 1 bonus chapter
This scene is from Mumen Rider’s school days when he tries to rescue bullies from punk. Mumen Rider is wearing a helmet, Perhaps foreign readers might think he was dressed as a hero from a young age, but that’s not the case. I will explain the background with the Japanese school system.
Students attending public elementary and middle schools generally live within walking distance. Since each prefecture has designated schools according to the area where they live
In urban areas, most students live within a 10-20 minute walking distance.
However, in rural areas, school allow some students who live far area to use bicycle for commute . Students are required by the school to wear helmets designed like the one Mumen wear in above scene. (He is a man who follows the rules seriously).
From the perspective of a Japanese person who grew up in an urban area, these school helmets give the impression of being a bit rustic.
(In fact, when I visited my mother’s home town when I was a child, I was surprised to see all the students wearing the same helmet on their bicycles in the town.)
Following article from Japanese news paper talks about students these days tend not to want to wear helmets due to design.
Now you can understand the meaning of this helmet and why Mumen wear it