One day, after losing his life in an unexpected accident, he was reincarnated into another world as Rain, the eldest son of the Proud Lord family, a local aristocracy. During his reincarnation, Rain received a natural talent for magic from God, and now he can use ``synthesis magic,'' which combines attributes, and tries to make use of that talent to live a comfortable life in his territory. but……! ? Aim for a comfortable slow life with Shiro, a young Fenrir you found in the forest while practicing magic! !