Standard synopsis: This world has never had a savior, only ordinary people saving one another. This world doesn't need a savior, either. We don't need one to come rescue us. If you don't mind the author's awful writing, I'll do my best to share a story filled with love and hope, and just a little courage.
Also known as "There Has Never Been a Savior"
The real synopsis: As someone who transmigrated to another world and failed to "invent" concrete or glass for over twenty years, Oulos thinks he's made a pretty poor showing of himself. Just as he's about to settle down as a half-native and live out a dull, boring "noble" life, he suddenly gets a younger brother who has invented concrete! And this younger brother has even stolen his right to inherit the title?
Ahem. It's basically a story about a transmigrator who's gotten used to another world, living off an elf's generosity and going around saving monster girls... probably.