Ordinary urban girl Xia Susu discovers that the old bathtub in her home hides a heaven-defying secret: it actually connects to the ancient miniature dynasty of Dayin, which has been completely submerged by a catastrophic flood. The once-prosperous imperial city has been reduced to a vast expanse of water, and the God of War Prince Chu Yebai, along with his young sister Chu Xiaoyu, remaining soldiers, and tens of thousands of commoners, are trapped in the monstrous floods, facing the constant threat of being swallowed by giant waves. Accidentally catching a glimpse of this catastrophe, Xia Susu cannot bear it and uses supplies from the real world to drop aid to the other end of the bathtub. Foam boards transform into floating islands on the sea, self-heating meals relieve the starving and freezing refugees, and all kinds of modern tools repeatedly resolve the life-or-death crisis.