Vanguard of Hell: World’s End

From the start, he massacres a city. Once he's built a Gundam, he wipes out an entire nation. Then he builds a magical perpetual motion engine and heads north to destroy the Giant Kingdom. After that, he returns home, upgrades the Gundam and the engine, sends his undead army west, the Gundam east, and the engine south to set the sea ablaze.

Didn't I say from the beginning that I wanted to write a story about destroying the world?