Estimated minutes: 5 min
Designer: Tomoaki Hamanaka
A flattened triangular pyramid whose apex solid angles are all 90 degrees. It is used as a fundamental element for forming the vertices of cubes and rectangular prisms.
Children

Asymmetric Triangular Pyramid
A triangular pyramid formed by deforming an obtuse triangular pyramid using a three-dimensional twisting fold. Its defining feature is a left–right asymmetric structure.

Cube
A cube with a band-like structure around its perimeter, serving as a structural isotope of the basic cube. Because its volumetric structure appears on the surface and remains movable, it can be easily transformed into other shapes.

Basic Cube
The fundamental cube form. A basic structure for understanding the relationship between faces and corners.