This may be kind of stretching the limits of YKTTW, but I'll give it a try anyway. Let's suppose there has been a successful video game series. The games are good, the fans love them, and everybody's happy. But this series that we're talking about here is not an RPG series, and the developers decide to introduce at least one RPG to the series. It could just be because the fans are clamoring for one, or because the developers want to try their hand at an RPG, or just because RP Gs tend to be liked for their depth. Whatever the reason is, there is an RPG that comes out for a series that you would not generally expect to have an RPG. Examples:
Hello, Unknown Troper. You'll need to get known to lend a hand here.