So This Is the Undead Calamity

[Chuunibyou Transmigration] [A Mouthy Smartass] [One Heroine] [No Cheats] Shen Yisi is tricked into transmigrating to a fantasy world where humanity has been forced to retreat to a small island. With too many people and too little land, humans survive by slaughtering and robbing the magical creatures on the mainland... The protagonist tries to lead his people in making a life on that continent, but the world is incredibly bizarre. Touch the nighttime fog and you die instantly. Sign a contract with the land and become a land-bound spirit. Some patches of land have nearly a hundred suns hanging above them...

The protagonist was only fifteen when he transmigrated, the perfect age for chuunibyou. If you find him constantly getting scammed and doing stupid things later on, remember that his mental age really is that of a chuunibyou teenager! Even when he discovers that the System is fake, he goes from despairing one second to fully revived the next. That's exactly what I think chuunibyou teens are like: no matter how badly they fail, as long as they believe they're the protagonist, they can bounce back full of energy! The top brass of humanity know the protagonist came from another world and are extremely hostile toward him. The protagonist of this world is Qian Xiao, the "heroine's" older brother, who is hostile toward the male lead.