I wanted to do something in a fantasy setting where the day/night cycles were ever changing. So there's no '24 hours' in a day. Sometimes daylight would last 3 hours and then night would last for 20 hours followed by day lasting 13 hours. And so on. But on top of that I wanted the characters to have two different personalities and skills that change come day and night. It sounds a bit 'much' but it sounded cool to me. So a group of people would band together for a typical quest but come night, their darker selves would come out, to work against their ultimate goal (or something).