18+ Gakuen Game Neptune: Katsudou Diary

Somewhere in a slightly different world line is the dimension known as Gamindustri. Neptune and her fellow goddess candidates are studying abroad at a human school to understand and learn about the humans they are protecting. A trial was given to Neptune, who had been spending every day lazily as peaceful days go by. The challenge is... to create a game?!

(Source: Kadokawa, translated)