Humanity in the late 22nd century. Entering the 22nd century, mankind began using hydrogen energy for the environment. Fossil fuels and coal were completely abandoned. Things seemed to be going well. However, after decades of operation, a problem occurred with the hydrogen energy generators. Hydrogen energy works by combining and separating hydrogen and oxygen to convert the resulting energy into various forms. But the machine that separates the water created by combining hydrogen and oxygen broke down. Water kept rising until it completely destroyed the machine. The machine that combines hydrogen and oxygen also stopped working. Researchers opened the separation machine to fix it, but as soon as they did, a massive torrent of water gushed out. To make matters worse, the combining machine, which had briefly stopped due to the water, started working again. The laboratory was submerged, and thanks to its waterproofing, the machine continued to create water using oxygen and hydrogen transmitted from space. Eventually, the lab exploded, and the water escaped. The machine, which steadily covered the earth's surface with 0.5mm of water every day, eventually submerged all low-lying lands, leaving only high mountain peaks. And there was one boat cutting through that water: the 'Yuram-ho.' It is an eco-friendly 10-person boat that uses water as fuel and emits oxygen and hydrogen. Only one person was on that boat: Kim Yunseo. Today, she floats alone on the water. But then, a mountain peak catches her eye in the distance. Wait, it looks like someone is there. As she gets closer, she sees a person barely standing. She brings the person aboard and checks their condition. How long has it been since she last saw another human? She is overwhelmed with emotion.