In recent years, the phenomenon of localized bursts of rainfall has increased in Japan. For this reason, collecting and sharing rain information quickly is the most important issue in terms of disaster prevention measures related to water disasters. XRAIN, which is suitable for the observation of localized heavy rain, enables high resolution observations and drastic shortening of observation times. However, the observation area of XRAIN does not cover all of Japan. Conversely, C-band radar, which is suitable for wide-area observation, covers the entire country of Japan, but it has difficulty to observing localized heavy rain. Both radars have opposite characteristics. For this reason, we examined a method that complements observation information from XRAIN with that of C-band radar to determine the rain situation in all of Japan, including localized heavy rain. In this study, we also proposed a method that synthesizes observation data of XRAIN and C-band radar and uses our proposed disaster prevention-oriented method. As a result, our method made it possible to display observation information throughout Japan, including localized heavy rain, in real time. The proposed method and implementation results are described in this paper.