Slime wa Saikyou Taru Kanousei wo Himeteiru: 2-kaime no Jinsei, Chanto Slime to Mukiaimasu @comic

In a world where one's entire life is determined by contracts with magical beasts... Zeke, a pauper who formed a contract with the weakest of them all—a slime—lived a life filled with regret and scorn from those around him. He eventually grew old and met a despairing end... or so he thought, until he found himself regressed to his childhood! Determined to give Fios—the only partner he truly connected with in his previous life—a better fate this time, Zeke resolves to turn his life around. Aiming to rise from a slum cleaner to the head of a grand merchant association, he sets his sights on the slime's "ability to dissolve anything." What's more, it seems his slime partner also possesses a hidden power...? This is a miraculous "relife" fantasy, where the regressed, weakest duo will dissolve the darkness of their world!

(Source: TO Books, translated)