The hematopoietic system is maintained by hematopoietic stem cells. HSCs are characterized by self-renewal and pluripotency, but their essential functions have not yet been elucidated. Using mouse, monkey, and human as models, we conduct interdisciplinary research by integrating the latest measurement technology and computational science, with the aim of understanding the essence of these cells. Understanding the nature of HSCs is expected to lead to the elucidation of the pathogenesis of aging and hematological diseases caused by the disruption of HSC functions. In recent years, it has become clear that the aging and abnormalities of HSCs are involved not only in hematological diseases but also in metabolic diseases and cardiovascular disorders, which are seemingly unrelated. It is expected to lead to the understanding of various biological phenomena beyond blood.