Bankrupt aquarium shop owner Chen Yu unexpectedly discovers that his old sea tank connects to the ancient East China Sea three hundred years ago. At that time, female general Shen Jinglan led the remnants of the Zhenhai Navy to be trapped on a deserted island, besieged by Japanese pirates and cut off from food supplies. Chen Yu uses modern supplies to cross time and space to rescue them, using fishing gear, lighting, and medicine to help the garrison survive in desperation, and relying on sea pearls to resolve real shop crises. Facing the massive invasion of Japanese pirates, he uses modern equipment to stage a "sea god manifestation" to rout the enemy, and also helps Shen Jinglan expose the imperial court supervisor's collusion with the enemy and treason conspiracy to retake the coastal defense. The two establish a cross-time-space marine trade, Chen Yu upgrades his small shop into a deep-sea curiosity museum, and deep within the fish tank, there are still vast unknown ancient waters waiting to be explored.