After Koganei was rejected by a girl he had confessed to, he angrily ran off and was hit by a car.
When he woke up, he found that he was reincarnated in another world as Theodore Goldberg, the eldest son of a marquis. And of course, as Koganei is no stranger to isekai series, he knows that he will have some sort of cheat skill to become overpowered and live a slow life.