World Goes Under, Empire Rises Up

The world rule comes first: tectonic upheaval pushes global sea levels up by about three thousand meters, drowning land civilization and leaving a deep sea apocalypse in its place. Anything safe is either a heavily reinforced vessel or one of the very few strongholds high enough to stay dry. Rowan Bancroft wakes up one hour before the tsunami that ends the old world, with the memory of having lived through what comes after. He uses the hour to cut off the family that had been living off him, walks away from them entirely, and takes what he can get, which amounts to one inflatable boat. Everything he knows about the coming years is worth more than the boat. He knows which supplies will be impossible to obtain in a month, which stretches of water will be survivable, and which of the fortified vessels will matter. He starts trading and building on the water while most people are still drowning or fighting over the first dry ground, and what he assembles out of scavenged hulls grows into a floating power in its own right.