Curiously, I wondered why many onigiri we see are triangular in shape, I found https://onlinemuseum.net/cuisine/onigiri/onigiri https://onlinemuseum.net/cuisine

Curiously, I wondered why many onigiri we see are triangular in shape, I found https://onlinemuseum.net/cuisine/onigiri/onigiri https://onlinemuseum.net/cuisine/onigiri/onigiri and others which seems to claim that this is because they're formed in the shape of mountains to drive off spirits. But if you ask me, this is either true or is simply another one of those things, where it happened so long ago that nobody really knows the answer for sure.