That Time I Got Reincarnated as a Disappointing Prince: Right Now I Can't Even Do One Sit-Up, but I'll Try to Lose Weight and Save the World

A young man who gets into a plane crash while returning from a business trip overseas is reincarnated into another world after being asked by the goddess to defeat the evil god. However, he was reincarnated as a stupid prince who is known among the aristocrats as the "Pig Prince (Orc Prince)" because of his fat and ugly appearance. If you can't even do one sit-up, how are you going to defeat the evil god?