Kamigami no Inai Hoshi de (Light Novel)

When I came to, it was the year 1990. I, Sumeragi Izumi, am currently in the Game club of a certain academic city in Tachikawa making an 8-bit & 16-bit game, very much enjoying my student life where a buxom senpai just moved in next to me… But, all of a sudden, I was entrusted with the creation of a certain planet as the “Representative of Humanity”!?