It's funny that you ask about that. The bags are called Randsoseru and are used from grades 1 to 6 in elementary school. The reason it's interesting is that about a month ago, my neighbor brought over two and asked if I could make something out of the ones her kids used to use. One was over twenty years old and the leather was unfortunately very cracked (and even flaking off). I just finished making a coin wallet out of the other one, and I made it in a design inspired by those backpacks. The red leather on the outside was cut from the outside flap of the backpack. The inside is a waxed Japanese leather.

https://www.aliexpress.com/item/32924186429.html?spm=a2g0o.order_list.0.0.124f1802H08UXdSure, here's a good one that I use. You can order it with 1mm holes. It's a great option.