There are so very many origami cubes, thought I'd start numbering them from the other end.
This one has a closure very like that of the 3×3 tato. You start by folding the four corners to the center and then dividing in thirds both ways -- no creases across five of the six faces, that way.
This compares size-wise with the waterbomb -- the waterbomb is one-quarter of the size of the square it's made from; this model is one-sixth×√2, around 0.2357023.
Plus, you can make a whole pot of jasmine tea with it. Lots of room for expansion.