Was it last year of the year before that cold brew coffee became popular. In Japan it’s called 水出しコーヒー and if you go to any coffee shop it’ll cost at least 400¥.
400¥ for coffee beans you let sit in water overnight. That’s a great deal.
Or…… buy this container with a filter. Buy your ground coffee beans, add water and wait. There are many recipes out there. I’m more of a try and see person for this.
If I were to buy coffee daily. Which I used to, this would save easily 300 a day. Even if you buy canned coffee this would save 100¥ a day easy.
Coffee grounds can be useful for somethings
Plus the added benefit is that you can use the grounds afterwards.
See posts garden, slugs.