From the Beginning of the Puzzle, a Savior Organization

In a world that is about to be destroyed in three years, a young man named Lí ēn is summoned back to life from death by a being from a parallel universe. Given a mission by his irresponsible parallel self, he is tasked with saving the world. His mission is complicated by a foreign swordswoman who speaks without thinking and a protagonist who mistakenly believes himself to be the main character in a boy's manga series, leading him to rush headlong into battle with a "Waahahaha" cry.