There's not a lot of things were said and shown, basically it's just an introduction and all that jazz.
So basically, this guy is like ZUN, who makes the whole games by himself. Here, the guy started to think that he's not needed in the company he worked at for 15 years due to changes in the industry and tries to resign. But the new employee, who was fascinated by the old game the guy made, persuaded him otherwise. But no dice, and MC pathetically dies like in one of the stories told by his drunkard dad, where a really stiff and proper old man who was living without fun died, when he was hit on the head by a turtle thrown by a crow. His dad mocked him for living the same way.
So the MC, Tohru Jin, is reincarnated into a body of a tomboyish loli somewhere in the forest around a village where demihumans live. As he guesses from designs and the tower looming far away, he is now in the world of a game he designed almost by himself (I chuckled when I saw his vision of elves, who are basically mofumofu people from Utawarerumono with a beauty complex). He, being a human who seem to be despised by the demihumans, gets caught and brought to a suspiciously looking priest to be an offering in the name of the Creator God, Tohru Jin (with a pun on his name 神 'God/kami' and 'Jin/shin'). And that's it, we need to wait for the next chapter to know more.