"Aruteido(?) no Mahou no Sainou" de Kondokoso Isekai de Slow Life wo Okurimasu

One day, after losing his life in an unexpected accident, he is reincarnated into another world as Rain, the eldest son of the Proud Lord family, a local noble family. Having received a natural talent for magic from God when he was reincarnated, Rain, who can now use "synthetic magic" that combines attributes, tries to use this talent to live a comfortable life in his territory, but...!? Aim for a comfortable slow life with Fenrir's young Shiro, whom I picked up in the forest during my magical training!!

(Source: Futabasha, translated)