By the Grace of the Gods (Manga) 12

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

Gimul will soon be celebrating its founding with a festival, and Ryoma decides to participate by opening a food stand with his Bamboo Forest workers. They'll be serving some special dishes from the varied hometowns of Ryoma's employees. As excitement builds up for the festival, a potential problem arises when giant ants threaten the road to Gimul. In response, Ryoma takes a job with the Tamer's Guild and deploys his army of birds and slimes to search and destroy the dangerous ants