The history of eigenvalue computing software development, starting with Earth Simulator 1 in 2005, has continuously evolved through the K computer, Fugaku, and Fugaku-next. The project code is called EigenExa. Humanity has already reached the Exaflops era, and we are now in the transitional stage of transforming computer architecture from conventional vector, many-core, GPU, to quantum gate. We would like to summarize our nearly 20 years of development. The applications currently being performed on Fugaku present one of the benchmark challenges to illustrate the maximum scale of computational feasibility. We can show that diagonalization of Hermitian matrices of at least 1 million dimensions is feasible with sufficient computational resources and that the boundary between dense and sparse matrices has considerably migrated.