By the Grace of the Gods (Manga) 07

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!

In his past life on Earth, Ryoma worked himself to the bone as an employee of an exploitative company. Now, in Seilfall, the former office drone decides to start a business of his own?!

Now that he's surrounded by tamed slimes and trustworthy staff, it's smooth sailing for Ryoma's business venture! Discovering new kinds of slimes and practicing taming magic with the Duke's family are only the start of the good times in store for Ryoma.