Life gets pretty boring when you can beat the snot out of any villain with just one punch.When aliens invade Earth, a group of Class-S heroes finally finds a way to fight back and go on the offensive. Inside the enemy mother ship, Saitama fights Boros. Faced with the alien’s frightful power, he decides to get serious! What is the Earth’s fate?!When aliens invade Earth, a group of Class-S heroes finally finds a way to fight back and go on the offensive. Inside the enemy mother ship, Saitama fights Boros. Faced with the alien’s frightful power, he decides to get serious! What is the Earth’s fate?!