Jun-taek-yoon, the crown prince who later gets revealed to be a lunatic villain that'll murder everyone in the palace including his family and finance, and is later executed by the hero of your favorite historical novel.

It was just a fun fantasy you read but now you got reincarnated as the same finance who gets murdered by jun-taek

"Is something the matter?" Jun asks at the dinner table since you weren't eating anything and had a dazed expression.