With the increasing imperative for carbon neutrality, gasification of carbon-based resources such as low-rank coal and/or biomass using fluidized-bed reactors has emerged as a pivotal process for generating clean syngas and hydrogen. However, conventional single-fluidized-bed reactors are limited by serious tar formation and low efficiency, which has motivated the development of staged systems that physically separate pyrolysis, gasification, and combustion. Japan has played a pioneering role in advancing dual fluidized bed (DFB) and triple-bed circulating fluidized bed (TBCFB) technologies, emphasizing reaction decoupling, thermal management, and process intensification. Unlike developments in other regions, Japanese research is characterized by the systematic integration of fundamental hydrodynamic studies, pilot-scale validation, and engineering innovations tailored to the nation's energy context. This review summarizes the theoretical foundations, hydrodynamic studies, pilot-scale demonstrations, and recent engineering innovations, including CO₂-assisted gasification, and new cyclone pyrolyzers, developed in Japan. Despite the challenges associated with scale-up and system complexity, staged gasification has been demonstrated to offer distinct advantages in terms of syngas quality, tar suppression, and feedstock adaptability. The future of this field lies in decentralized, small-scale distributed systems integrated with the combined heat and power, in alignment with Japan's carbon neutrality roadmap and providing global insights into sustainable low-rank coal and biomass utilizations.