Question; what even is "natural ice"?
Natural ice is ice that, instead of being frozen in a freezer, is frozen outside in the cold. They draw in water from nearby springs and leave it out to freeze in the open air while making sure that stuff like dust, snow, leaves, etc. doesn't get stuck in it. According to a website I found, it can take between 2-3 weeks for the layer of ice to be thick enough to be harvested and cut into smaller pieces. Not really sure how it's supposed to be different from normal ice but apparently it's more clear and it has fewer impurities. Probably just another Japanese obsession that something artisanal is better even if it takes three weeks to get some ice.