Two-dimensional materials such as graphene can be stacked by van der Waals forces with arbitrary control of materials and angles, giving rise to a major paradigm shift in materials science because it provides a synthetic method that is not bound by conventional bonding. Furthermore, a unique two-dimensional nanospace exists between the layers of stacked two-dimensional materials, which can be the stage for new science. Therefore, by introducing the new ideas of “degree of freedom of accumulation” and “two-dimensional nanospace” to diverse two-dimensional materials, this field proposes “2.5D materials science: a paradigm shift in materials science toward social transformation,” which is a great leap forward from conventional research. In this field, we symbolically express the new possibilities of two dimensions plus α as 0.5 dimensions, and through an all-Japan structure, we will develop research that will revolutionize conventional materials science.