You wanna know one of my writing quirks? It's quotation marks. I hate using them, but no matter what, there's always a conversation between characters and I have to use them. I keep forgetting to put the punctuation within the quotes. In fact, I did that for the longest time before my mom finally pointed it out to me a few months ago. xD It was ridiculously hard to break that habit, but I think I've got it covered... I think.
Anyway, my main point it that it helps a lot to reread chapters very carefully. I can read my chapters twice and I'd still miss little tiny mistakes, such as minor typos or maybe an extra comma, or such.
I think you should focus your time into the next chapter, when you have time, though. I hate how much time school requires. It eats into your day leaving you with only a few hours of free time, if you include the time it takes to complete homework. I'm looking forward to the next summer vacation already. xD
I'm not really the person you should be going to for a full-on critique. I barely have time to work on my own fic right now, and you wouldn't want a rushed review, now would you?
But from reading what you have, I say you need the most help with sentence structure, grammar, and formatting. Description comes next. Your first chapter describes a glorious evening, for example. How so? Why is it glorious? (As a note, the way you described Mightyena is the way NOT to introduce a character. A list of qualities is lifeless. You can comment on Mightyena's size and fur color, but don't forget that you're dealing with a moving, breathing character that has a purpose and desire.)
Your chapters are really short too. Longer chapters (generally) are more plentiful. (But don't count Word pages: focus instead on story and proper formatting, and end it only when the chapter needs to end.)
Your first chapter should be written in such a way that the reader gets intrigued by your story. (All of your chapters should be interesting, but the first chapter carries the most weight, since it's the way the reader gauges your writing ability, and the way they decide whether they want to keep reading or not.) And if you have a really short chapter, then the reader won't have time to get immersed in the story and characters. In other words, they won't care.
The conversation between the Umbreon and Mightyena could have been greatly expanded, since (I'm assuming) it's the basis for the chapter. It's perfectly fine to center a chapter around a conversation, but you have to make it interesting.
That's all I can say for now. For more help, I suggest requesting a review from a more experienced author on the forums. I can't dedicate my time to this right now, but if you have a question about anything I said just now, PM me.