When not so normal man transmigrates into a novel that he didn't even remember its title, as a short-lived extra with immense potential, talent and perfect looks.
If he has gotten only good stuff, he would die from joy, but nothing comes without a price. He lost most of his emotions, desires and sensation of pain.
He thought it was a blessing and dreamed of just ignoring the bleak, apocalyptic future and doing what he wants without feeling an ounce of guilt. But after a few days, he understood that he would go mad because of the boredom that for some reason didn't reduce like his other emotions.
Therefore he began to think about what to do about his problem.
“Kill everyone to prevent apocalypse!” Though this is a good idea, why would i kill everyone because of the apocalypse? Although killing everyone would prevent the apocalypse, how the hell i will endure the boredom when all of my entertainers are killed?
“Seduce and manipulate important people with his handsome looks and use them for his benefits.” Well, i can do this but it isn't enough.
“Pamper his prodigy sister to make her dependent on him in the future to use her overpowered magic to find a solution to his curse.” Hmm, that's good, but this too isn't enough.
Let's combine these last two.
An apathetic brother who searches for a way to lift his curse while doing strange things to endure his boredom and a yandere sister who is trying to hold herself back from killing the woman/man who was seduced by her overly handsome/beautiful brother.