The Komebukuro form lends itself well to a lot of variation. The squares can be made into rectangles, as here, to create a longer or rather taller bag. 
As shown here, the Japanese rice bag is simply two sets of vie squares — a base and four sides. The bag sides are sewn to the base, four straight stitches. Then you sew the four sides to each other, one edge at a time. the result is sort of a box or five-sixths of a cube; you could add a zipper and a lid fairly easily to this design, really.
In the photographs here, I’ve shown as best I can what I’m talking about. The gray fabric in the middle is the BASE of the bag, while the floral print in gray are the sides of the bag. I’ve laid out the fabric of the liner in all floral print, while the outside of the bag has a single white panel where I can write my name, or the name of the person the bag is for. Embroidery could be done here, for someone who was particularly ambitious.
Seven inches appears to be a good size for the Komebukuro. You can get a lot larger than that, of course. You can also get a lot smaller, but there’s a point of diminishing returns under about five inches on a side for the squares that make up the base and sides of the bag. I also don’t tank I’d want to go much larger than a foot on a side. More than that would be unwieldy, and you’d be better off with two or more bags.
Back to construction…
Once the two boxes of the inner and outer bag are made, they are nested, and the top edges are folded down and in between the two bags. We then top-stitch the seam between them. As ive discussed elsewhere, the last step as the sewing of the eight buttonholes.
There’s a picture, here, of the outer shell of the bag already assembled, but still inside-out. This is to show inside-out construction. When building a bag, the fabrics are sewn right sides together. This puts the seam on what will eventually be the inside or in-between space of the bag, between the liner and the shell.
Then you sew in the button holes. Each side of the bag is now two panels of fabric, the shell and the liner. Each of those panels takes two buttonholes, which are maybe 3/4″ down from the top edge of the bag, and evenly spaced on the bag’s walls, about a try of the way in from the corner. The corners of the bag’s open top should be fairly visible. Threading a cord or a ribbon through the buttonholes creates the closure mechanism, but also creates a carrying strap.
My sense of this is that it’s fairly easy to vary the size of the squares into rectangles. But the square that forms the bottom or base is fairly rigid. You can’t alter that from a square too much without unbalancing the bag as a whole, I think.
This would look stunning in indigo-dyed fabrics, or with Japanese embroidery patterns done on the outside of the bag (doing them on the liner would create all sorts of things for your keys or other objects inside to get hung up on; stick to the outside). Many of those patterns are based in triangular geometry, so there is some real potential for elaborate, hands-on mathematics here.
My mother has made several of these bags, without the button holes or cording, to use as trash cans for her art studio. Paper and beads and parts that can be recycled go in one of the bags; while trash goes in another. They’re prettier than regular trash cans, and collapsible. She can fold them up and put them away when they’re not in use.
I may have to make some of my own for that.
All in all, I think I’m going to make a lot of these, both with with and without cording, in a number of sizes. They’re a good size for kids’ lunch bags, for example, or for an art kit for the car, or for portable storage of related items while camping. I think I’m going to try making some in 10″ and maybe 14″ sizes, but I think that a shoulder bag or something like that will work better as another project for teaching sewing for school books.
