I Was Mistakenly Called the Son of God and Forced to Save the World

"I died and was summoned by the goddess, but I was told: 'Sorry, I called the wrong person. Your childhood sweetheart is the brave one.'" "What? You want me to save the world on her behalf? Can't you give me the power of a hero?" "Oh, demigod protection? Okay, then let me use 'cheating level' magic to blast this fate into pieces!" ——Being cheated at the beginning, reborn at full level! See how the good-for-nothing Son of God changes his destiny against the will of heaven!