Ordinary office worker Takebayashi Ryoma (voiced by Azusa Tanosho) has hardly had a comfortable day. He is still single at the age of 39, working like a slave for a greedy boss in a black-hearted company. Finally, in a narrow and damp single apartment, his life came to an end. However, when Ryoma opened his eyes again, he found that he had reincarnated into a different world and became an 8-year-old boy. Compared with the dangerous real society, life in the different world is hard but full of fun. Ryoma lives in the forest and studies how to use magic to tame wild slimes. In this world, Ryoma quickly made friends with the cheerful daughter Arya (voiced by Yuki Kuwahara), the Duke Reinhardt who likes to wield swords (voiced by Daisuke Ono), and the kind and enthusiastic monster master Alisa (voiced by Saori Hayami).