Kami-tachi ni Hirowareta Otoko By the Grace of the Gods
Only 39 years into a life full of bad luck, Ryoma Takebayashi passes away in his sleep! Taking pity on him, three divine beings show compassion by reincarnating him as a young boy to a magical, new world.
Now he spends his time researching and caring for slimes. But after healing an injured traveler, Ryoma decides to set out with his new friends on a journey to use his power to help others.