FanFic A Good Way to Kill a Month's Worth of Free Time
I found this story via T Vtropes, having never played Dungeon Keeper and only watched the first three episodes of Sailor Moon before moving on, so I can't comment on Dungeon Keeper Ami's fidelity to either. That said, the author does a very good job of quickly establishing Ami's abilities in a way that makes sense without it feeling like an info dump, meaning even people like me can enjoy the story.
The story itself is not the pinnacle of literary achievement. It is very obviously a fanmade work, complete with technical issues, uninteresting side characters, weak character development, and forgotten plot points. However, it also has the ability to capture and hold your interest such that you will want keep reading until the end, despite the door-stopping length. It's quality comes from placing a very stereotypical character in an equally stereotypical but diametrically opposed position, simultaneously deconstructing both.
It also examines what happens when a guile hero is also incredibly powerful. By virtue of being Sailor Mercury, Ami has powers beyond a normal Keeper's. However, she is limited by her nature, which forces her to find new ways to do things. She may be powerful enough that, were she to do things traditionally, she would likely win, but it is far more entertaining to watch as she finds new ways to use, misuse, and abuse every ability she is given.
What is remarkable is that even as the plot spirals out of control and the setting grows to immense sizes, the story's quality only increases. Many authors have trouble juggling complex and competing agendas, but Dungeon Keeper Ami's writer seems to have the reflexes to do it, resulting a world which, despite being populated by underdeveloped and uninteresting characters, feels very much like it could be real.
The story is very, very plot driven with little time spared for character development, and Ami's newest scheme is more interesting than the characters involved, but you won't notice or care about the problems because you'll be too busy reading the next chapter. Given the story's length, I suggest bringing snacks.
Fanfic Amateurish, yet awesome
Dungeon Keeper Ami is far from a literary masterpiece. The writing style is sometimes awkward, the characters themselves aren't particularly interesting, and some of the chapters could have used better proofreading. If you're looking for something deep and profound, you won't find it here.
Enough about what you won't find. What you will find is a plot that will keep you needing to know what happens next, exciting action sequences, well-timed comic relief, and tons of Crowning Moments of Awesome. Ami is and is faced with one impossible challenge after another, and through a combination of knowledge, planning, Science, determination, sheer luck, and the ability to think like a Munchkin, manages to overcome all of them in increasingly awe-inspiring ways. If that sounds like something you'd like to read, then consider Dungeon Keeper Ami recommended.
The only other problem is that, as of right now (July 2, 2012) it's reached Doorstopper-length and still incomplete. :(
Fanfic Unattributed comment
The author has a priceless Omake located here
in which Ami scams Metallia in a manner that has to be seen to be believed.
Fanfic Comment by Shay Guy
Note that due to the branching, collaborative nature of the site, the linked page, despite being the first marked "Dungeon Keeper Ami" and second posted by Pusakuronu, is not the first in the story; that would be this post, written nearly five years earlier. Also, the linked post has multiple options available; the "canon" choice is 'As above, but "Where did these bug-eyed things come from?"' (For all successive pages, just click the option in bold text; as of this writing, there's one other fork, and someone might post more, but just backtrack whenever you see anyone else's username.)
Fanfic Comment by Sun Tzu
Pusakuronu makes fairly impressive use of Magic A Is Magic A, allowing Ami's intelligence to become an important edge... and one she sorely needs. The update rate itself is pretty impressive, with a new chapter coming out every 3-4 days.
Fanfic A protagonist worth cheering for
At its Heart, this story is about Ami facing and overcoming great struggles.
There's the moral dilemmas associated with her position, from "How do I defend myself against people with good intentions who nonetheless want to kill me?" to "Is it worth giving a small service to a dark god in order to free people from eternal torture?" There's the direct struggle for survival, with the forces of both Good and Evil wanting to bring her down. There's her overarching and lofty goals to defeat the dark gods and fix the world. And set against these, there's her intelligence, her courage, her magic, and an assortment of both Good and Evil followers.
Despite the bizarre premise, mashing together a magical girl anime and the darkness of the Dungeon Keeper world, it's a compelling read. Ami is just someone you want to cheer for, as she finds her way through everything the worlds can throw at her while clinging desperately to her principles. And it's woven together with plenty of clever humour, heartwarming moments, and concentrated awesome (ever seen a chlorine trifluoride fire the size of a skyscraper?).