That Time I Got Reincarnated as a Slime

Salaryman Satoru Mikami throws himself in front of a knife to save his colleague, and is reincarnated in a fantasy world as a slime. After an inderminate amount of time wandering around a dark cave, he finds an imprisoned dragon who teaches him how to see using magic and names him Rimuru Tempest, and in return, the newly christened Rimuru absorbs the dragon and its cage in order to figure out how to free him, no matter how long it takes. Finally able to see, he is able to leave the cave, and Isekai shenanigans ensue with an OP protagonist who stumbles his way into forming a new, prosperous country.