Southeast Asia is one of the regions most vulnerable to natural disasters in the world. Natural disasters originate from external forces acting upon society, but they become disasters as a result of complex interactions with various internal factors within society. Furthermore, disasters are a process, and societies vulnerable to disasters share the common factor of vulnerability to conflict. On the other hand, it is known that the occurrence of natural disasters can provide opportunities for fostering peace between countries, as well as within disaster-affected countries. This chapter focuses on three elements that contribute to peacebuilding through disaster response and preparedness: “the cooperation among the people sharing the same disaster memory and threats”, “the existence of relief and reconstruction funds (from international society, etc.)”, and “the opening up of relief activities to external partners.” Within Southeast Asia, cooperation among Red Cross and Red Crescent societies in the region is a means of achieving these three elements in disaster response and preparedness. Such cooperation among RC/RC in disaster response and preparedness holds the potential to contribute to mutual understanding and peacebuilding by leveraging shared experiences and resources to establish cooperative relationships through the disaster process.