By the Grace of the Gods 02 (Manga)

Slime's up for one recently deceased middle-aged businessman! When the gods reincarnate him in another world as a boy with magical powers, he discovers that magically-tamed slime are an untapped natural resource!

After office worker Ryoma Takebayashi dies, three gods ask for his help and reincarnate him as a child in a parallel fantasy world. Ryoma enjoys his slow new life of patiently taming and researching slime, but after three years of living alone in the forest, he meets a kind duke ...