Gas turbine combined cycle (GTCC) and steam power generation systems are among the main products of Mitsubishi Heavy Industries, Ltd. (MHI). Looking at the accelerating global trend of energy transition, there is an urgent need to make these products carbon neutrality as well. The development of the key decarbonization technologies for thermal power generation is carried out in the Takasago and Nagasaki districts in Japan where our corporate machinery works and laboratories are located. In the former district's Hydrogen Park Takasago, we are working on the creation of an environment for long-term integrated demonstration of elemental technologies under actual operation conditions. On the other hand, the latter district, the Carbon Neutral Park Nagasaki, functions as the important area of our elemental technology development activities. This report introduces these parks, together with the summary of the technologies being developed therein such as hydrogen production.