The 8th Son? Are You Kidding Me?.

Ichinomiya Shingo, a 25-year-old man working at a firm company, while thinking of tomorrow's busy working day, goes to sleep. However, when he woke up, he found himself in a room unknown to him and realized that he is inside a 6-years-old body, taking over his body and mind. He soon learns from the memories of the boy that the boy was born as the…