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It's an AU starting from a little before Mahorafest. It's supposed to be Chao's original timeline. Except that in it Negi gets turned by Eva and so a future stalker of his and Eva's Arch-Enemy shows up to assist Chao during Mahorafest.
The story shows us some of Eva's past and how it's going to affect Negi, him being her disciple. Something which wasn't really shown in the manga or many other fanfics so that's cool.
He even gets some fledlings of his own.
It focuses on different girls than the series did.
The Dark Mistresses that show up are characters not just designated villains.
It's even got it's own <a href='http://tvtropes.org/pmwiki/pmwiki.php/Fanfic/FangViceAddiction' target='_blank' rel='nofollow'>tvtropes page</a>
It's not perfect, because sometimes it is confusing or a bit irritating that you're being shown Eva's past in media res when what you want is to continue the action from the last chapter and have to read through it before you get back to what you want, but it's not bad in itself.
It's been a while since I read it. I saying right it now I'm not gonna cry. No matter how sad it is.
Also some other things are developed on like mixing light and dark, like you would Magic and Ki.
The chapter are also fairly long. So I would recommend it.
Does that answer your question and bit more thoroughly?