I say unusual in the sense of Japan seems to be the only one to have solved the issue of how do you transport 2 kids on a bike not with "big box" like the dutch and subsequently the entire western world but via 2 seats, they're apparently very popular over there as a means of transportation.
I've only seen a person wearing a helmet in Japan exactly once. I asked him about it and he says it was for seizures.
In fact I went into a trek store one time in Japan and they didn't even sell helmets. They're not big on them over there for some reason.
Edit: sorry, I didn't realize I wandered into a helmet struggle session? Why are we even doing this lol. Wear your helmet. Always wear one.