What Do You Mean, He Speaks with Heaven's Authority and Rules for Eternity?

As a chuunibyou shut-in studying acting, Li Ang had always wanted to say that transmigration was just something made up in anime, comics, and games. That was, until he woke up one day and was hauled off the ground by a strange swordsman. Oi, use that invincible rodent-control technique of yours and think of something! What rodent-control technique? Think of what? Why are you cosplaying as Reinhard van Astrea? Have aliens invaded, has World War III broken out, or is the world ending? Wait... What do you mean goblins are invading?