On Pokemon Sun and Moon's website, Shigeru Ohmori, the director of the games, talked about a few aspects of Sun and Moon. Here are some highlights:
On why he chose Sun and Moon as the title names:
In these titles, what I wanted to express is the brilliance of life and of the relationships between humans and Pokémon as they influence one another. That is why I chose to name them after the sun and moon, which have so much influence over our own Earth.
Why the two titles take place in different worlds:
Between Pokémon Sun and Pokémon Moon, there is a time difference of 12 hours. This was our first attempt at making such a great difference between two game versions. In the Alola region, the Pokémon that you might encounter on the same route can vary between day and night, and so this time difference allows players to have a completely different experience.
Why the focus on night and evening:
To show the Alola region’s rich nature and beautiful towns, we were very particular about the lighting. Thanks to that, the same location can have a completely different appearance depending on the time—sometimes wrapped in the gentle glow of moonlight, sometimes illuminated by the crimson of the sun setting over the sea.