All of his attacks are always themed after rain. Westerners may not understand all of the cultural references
The soldiers create rain of arrows, the move literally have the word "rain" in the name. And in East Asian culture, dragon is a symbol of rain. The Dragon Gods are responsible for creating rain and adjust the amount of rain for each region. In Mudano's previous fight with Tsukuyomi, he created the Shinto Goddess of Rain.