Apocalypse Zero

The survivors are doing whatever it takes to survive in a world gone insane after a sequence of natural disasters had reduced the world to ruins. But one young kid, Kakugo, who was gifted by his late father with incredible martial arts skills and a super-strong suit of armor, has been given the responsibility of making the world—or at the very least, his school—a safer place. But his sister is on a quest to make the planet peaceful... by destroying humans, and she possesses the same set of abilities and tools!