Guy was reincarnated as a slime and named himself Rimuru Tempest. While contemplating his life on the cave, he has met the great dragon of chaos, Veldora, who was locked up, and has made himself be his sworn friend. In order to free him, he has journeyed and met countless of comrades who'd one day be with him as he create his own monster country.
SUPERB MANGA! Rimuru is such an overpowered cutie slime. World building is a must!
Tensei Shitara Slime Datta Ken