An earthquake occurred in Central Sulawesi Province, Indonesia in September, 2018. It killed about 4,500 people by Tsunami which attacked within few minutes from earthquake and by huge landslides brought by liquefaction (Nalodo), which is a rare phenomenon in human history. The author, who was dispatched as JICA Expert to National Disaster Risk Reduction Agency in Indonesia, assisted Government of Indonesia in composing Reconstruction Master Plan with the help of other JICA Experts, Japanese academic researchers and consultants. In this process, the author gave technological explains of Tsunami dike and clarified the mechanism of the large-scale landslide by liquefaction. The result of dedicated efforts by Japan had Government of Indonesia entirely rely on Japan when they faced or disaster risk reduction policies such as large-scale floods. The author analyzed the reason why Japan got trust of Indonesia, and provided a helpful perspective on Japanese Official Development Assistance.