Plot = 6.9: Okay, I'm going to start this section off by saying that the story uses a lot of assumed knowledge; that is, it assumes the reader knows the characters/styles/locations talked about. This is fine for the Avatar part (in regards to things that the reader is already explicity aware of, such as 'Korra is the Avatar' and 'Raava is evil'. The author still needs to expand on things such as characterisation in the story), however it made the story somewhat difficult to follow for readers who don't know what 'Chitose Gen' is (including myself).
There are elements constantly being introduced that would seem fine for readers who know what Chitose Gen is, but for many, they're on here for Avatar; when you introduce new elements constantly, and without explanation, a reader gets left behind and is less willing to try and decipher the story you're trying to tell.
This can still happen with the Avatar elements, too. It's important to ease readers into a story; it is up to you to paint the picture. When reading, people don't want to have to look deep in order to make sense of it.
Characterisation = 6.5: This was hard to gauge as I know that many of the characters are from another fandom, and I don't know anything about it. However, that in itself is a problem; I don't knkow who these characters are, beyond 'good guy, evil guy'. The Avatar characters are also characterised in a similar manner. There are no truly defining features.
One thing I noticed was the way everyone spoke. It may be me playing a lot of Pokémon lately, however I found the dialogue (especially that of Eon in chapter 6.1) to sound a lot like one of the trainers who stand around Vermillion Forest waiting for you to have to walk past them. In essence, it sounded scripted—unnatural—and didn't give the speaker a lot of personality. Once again, it's a little detail that seems insignificant but helps readers believe in the character and understand their personality a little more.
Believability = 6.5: It's hard to judge this story as it was occasionally difficult to follow due to the formatting and unknown fandom (see 'plot' and 'technical writing', respectively). That being said, there were some definite things I noticed, mostly relating to the introduction of people/items/plot elements that seemed random. One of the major plot points that appeared out of the blue was the 're-rise' of the Equalists. When people get new protagonists, they come to expect new antagonists, too. The Lieutenant was one aspect that seemed highly unbelievable, as the readers know how disillusioned he became with the Equalists before the end.
Another is the strange new powers available to Korra, and the new characters that belong to the other fandom. How come Korra can suddenly use them? What are they? What is a Shingan? Or a Kekkei State? These things need more explanation; a brief overview doesn't suffice.
Technical writing = 5.0: There were a few spelling mistakes, however overall, this section was good. Grammar was also well done, and the only consistent punctuation errors I could see were missing commas, such as before and after names in dialogue, and a slight overuse of exclamation marks that can be distracting and lessen the overall effect. There were a couple of improper punctuation marks, such as using a semi-colon (;) when a comma or dash should be used, and vice-versa. These are only very small, and as you write more, you'll find that these errors won't come up so often.
The formatting takes a dramatic turn for the worse from chapter four and onwards. There are great big clunky paragraphs that make it hard for a reader to both stay focus and understand what is going on. All they see is a great big chunk of text. This text is also improper English. A new speaker must be on a new line. If Korra says something and Mako replies, his reply cannot just run on from hers. There must be a gap. On the wiki, this is used through paragraphs, however in physical novels, it's usually indentation.
The last thing I'm going to mention here is the shifting tense. It didn't happen often, but it was still enough for readers to trip over the sentence. Be careful when writing a story that you don't change between past tense (was) and present tense (is). Usually, stories are written in past tense as it is easier.
Non-technical writing = 6.9: There is nothing really wrong with the way this story is written. It's all logical and legible; what brought this mark down was the lack of description. A reader needs to be able to, not just see what's going on, but hear and smell and touch. This story has a very linear 'A –> B –> C' progression, which is fine, but there's no fluff. As a consequence, there's no foreshadowing of events to come, which can make unexpected occurrences (see above) more of a surprise and less believable. Fluff is fantastic in stories. It's the chocolate chips in a cookie. Balloons at a party. Leonardo DiCaprio. Fluff is what gets people excited and coming back for more, because it's not always the most important to the story (or cookie/party), but it's what makes it enjoyable.
The action was one other thing. There is a lot of fighting featured in this story, simply due to the type of story it is. There is bending, and there are also a few techniques not seen in the Avatar world. Unfortunately, lack of description in this section also damages the story. We want to know exactly how the enemy incapacitated our hero. Did he use a side-kick to send powerful jet of fire at them? Or was it a feint and the real attack was his left hand, engulfed in flame? These details are all important in an action scene.
Organisation = 6.6: It was hard to follow at times due simply to not being aware of what the cross-over fandom was about. The time-frame that this story covers is not clearly defined, and some sections seem to move too fast. One reason could be the short-cuts taken within the chapters by simply introducing a new section. As stated above, the plot can be hard to follow with all the new concepts, and without being eased into it, the reader is just left behind.
Total score = 6.38
My advice: I really don't want the score to discourage you. You have a story in your head; now you just need to work out all the details and help the readers see what you see a little more. Work on the characters' introductions. You obviously know what you're talking about, but many readers don't. We don't know who they are or what they look like. We don't know their history or backstory, and it's really something that we should be made aware of. An easy way to do this is to just add a lot of description; instead of just titling sections of the chapters with the setting, describe it. It helps the reader immerse themselves in your story, and it makes it easier for use to imagine the world you want use to.
Another note is to just format your chapters to make it easier to read. A page of text is always off-putting, regardless of what it's actually about. You want to encourage people to continue reading as much as possible.
Why I enjoyed this story:I really like the creative way in which the two fandoms came together. No, I don't know anything about the other one, however there was an interesting use of concepts that aren't present in Korra that seems to fit in. As said, just elaborate a little more and you're good to go!