Seichou Sokushin to Ganbou Cheat de, Isekai Tensei Slow Life?

Rucalt was reincarnated as the second son of an aristocrat after saving a girl from a runaway truck and dying. God bestowed upon him a cheat ability that allowed him to gain any skills he wished for. In addition, he could easily level them up with just a bit of use. By the age of three, he had gained the strength unparalleled that of all heroes in history. Nonetheless, he did not flaunt his powers, instead choosing to lead a life of freedom happily with his family in this other world! Source: AlphaPolis