5 needed to calculate an average
A year after their spaceship crash-landed on Earth, the alien species known as 'DearS' have been accepted into the Japanese citizenry. They are adored by many fan groups and trusted by most humans - with the exception of Takeya Ikuhara. Kind-hearted but resistant to change and skeptical of the DearS' seemingly-friendly behavior, Takeya tries to have as little to do with them as possible. But after he saves a girl from an incoming truck, and she turns out to be a DearS, Takeya ends up being far more involved with them than he could have ever imagined.
DearS is quite similar to Fantasy Maid in many ways. In both series some average guy comes into possesion of a non-human magical girlfriend who is completly devoted to him. In both cases the girl comes from some sort of mostly-female race which forms contracts with humans. In short if you read Fantasy Maid, you'll find many familiar themes (more than just the ones I mentioned) in DearS and might even like it.
A guy wrote down his "ideal" girlfriend and POOF for some reason she came into existence. But while she loves him nearly unconditionally, he is reluctant to love her back, because he already has a crush on someone else (read love triangle). That's more or less the plot of both of those series, so fans of one of them might find the other interesting too.
Note: Kono Kanojo wa Fiction desu has bits of ecchi, while Fantasy Maid is awfully cute (and a bit smut later on).