First, I must say that the title, 'Longing for a Pulse', is really captivating and unique.  It is suitable for your story and it's attractive to readers.   But I think it would be even better if there are more parts of the story that is related to the title.   The story seems to be only describing the events happening.  I think you can really add in the title as a metaphor in some parts of the story or even explain it a bit if possible.  If you add a few lines describing the connection between the events happening and the 'longing', it would be even clearer to the readers. 

The description is nice.  The way you mixed the two songs together is just simply great.  The lyrics that you picked fit the story perfectly.  The description is simply clear and precise.  It also gives off some hints of the story which just makes the readers even more curious about the story.   After reading the story, I felt that the quote that you wrote in the foreword, from Scott Westerfeld, is very true and it suits the story very well indeed.  But I think that the lyrics should be in quotation marks just like the quote from Scott Westerfeld, so that you're still crediting to the lyricists.  Overall, the description part is well done.

The foreword is great too.   I agree that "We hope for beauty and happiness in life but all that comes through is longing."  It's totally relevant to Kai and Ha Neul's story.   This sentence is aptly picked as well, Every heart needs a pulse to beat and every person needs a reason to live.  It is heartfelt and is echoing with the title.  Also, the way the clouds and the blue sky represent Kai and Haneul, and how they strive for each other's happiness, matched this sentence perfectly. 

Well, about the plot, I think that it's touching and simple.  It's not very original, but it is still not often to see a fanfic writing about the the hardships that a family is going through.   

However, about the flow of the story, I think that the pace isn't really even .  The first few chapters of the story are a bit slow.  I understand that the story need some time to build up the tension and to tell the background of the characters, but it seems to be repeated and a bit too long.  For example, those parts when Kai is trying to make Ha Neul talk to him can be shortened a bit.   Moreover, in chapter 3, where Ha Neul's thoughts are revealed, some of them are repeated.  I like the way you used shorter sentences and a different format to present Ha Neul's thoughts in that chapter, however, I think that you can simply use the more significant ones and not all of them, since it's a bit excessive.  The flow of the last few chapters are just right, and the plot is developed in a regular speed.  Moreover, I like chapter 11, since there's a little surprise in that chapter.  The death of Ha Neul is unexpected and I never thought that you'd make her die... :'(  But well, the chapter is sad yet surprising so I quite like it. 

For the grammar part, I think that you still have a lot of room for improvement.  It isn't bad, the story is readable.  The grammar part didn't affect the flow of the story, and I can still understand what you have written.  However, it'll be perfect if you can use correct grammar too.   There are a few mistakes that you often make.  First, is the tenses.  You often mix up the present and the past tense.  Second, I found out that there are more mistakes in chapter 3, in those diary entries.

In this entry,

"It's okay. Everything's going to be alright.

Pathetic. We won't let it go even when we are hurt.

We continue to hurt and keep hurting. 

Why.

I don’t know but I think I’m that kind of person.

19 Jun 2012"

In line 3, I am a little bit confused, since it's Ha Neul's diary, line 3 sounds like she's hurting someone instead of she's getting hurt.  So I think that changing it into

"It's okay. Everything's going to be alright.

Pathetic. Won't let it go even when we are hurt.

We keep on getting hurt and there's no end to it.

Why?

I don’t know but I think I’m that kind of person."

will sound better.  I mean it's just a bit confusing, but if you like the original line 3 better, then it's fine.

In this one,

"I know I have to sacrifice myself.

No one’s willing to do that.

So, even if I don’t want to, I have to do that.

I already said that I don’t want to do that, but no one cares about it.

So, stop whining about how people treat you and just shut up.

Suppress you feelings inside because no one cares about them.

Just don’t be hurt and don’t cry too much.

10 Jan 2013"

"I don't want to do that" is repeated.  It is clumsy and kind of repeating the ideas of the other entries.

The use of vocabulary is fine.  The choice of words are okay, and it's understandable.

As for the way you used Kai's perspective to narrate the whole story, I think that it is special, since most of the time, authors will choose Ha Neul's POV or the third POV.   However, there's one negative point when using Kai's POV.  Since this story is more revolving around Ha Neul, using Kai's POV will be hard to really let the readers feel what Ha Neul feels.  This affects the tension and it gives off a feeling that the characterization of Ha Neul is not enough.   Though through her diaries and her actions, the readers can still try to guess what her feelings are, they are still somehow blocked from Ha Neul's mind.  Therefore, I would suggest you to use the third POV. Using the third POV, you can both describe the feelings of Kai and Ha Neul.   But I think you did a good job in using Kai's perspective.    Anyways, I think that using Kai's perspective is a good try, and I do think knowing the thoughts of a bystander and not the main character is not most of the authors' style, so it's a unique choice. 

Moving onto the characterization part, I think that the characterization of Ha Neul is fine.  As for Kai,  I can feel him being hopeless, just like Ha Neul, since he can't change Ha Neul back to her original self.  However, it's a bit strange to see that he suddenly hates Ha Neul so much when he found out that Ha Neul is one of the elements that made his parents die.  Of course he will be sad and perhaps cry over this, but Kai, the over-protective brother, to fume at her just because of this and forget about she's still hurting is a bit over the top. 

I also like the way you name every chapter.  It gives off a little bit of what the chapter is about and it pushes me to finish the story in one go.  But the last chapter's name is kind of giving out too much information.  I would like to read the ending to find out whether it is a happy or a sad ending rather than knowing it before I've even read it.  It kills the surprise.  Just putting 'ending' as the name of the last chapter would be fine because the content of the ending is already out-standing enough.

Just one thing that I don't quite understand is that why does Ha Neul told her class about the tragedy?  Why does she do this?  At first she says she wants to hide the tragedy away but then suddenly tells the class about it?  

On the whole, the story is interesting and touching.   When I was reading, I could really feel Kai was getting frustrated with Ha Neul but somehow the feeling of Kai desperately wanting the old Ha Neul back wasn't strong enough.  I feel that you've really given a lot of hard work into this story, and I really like the story.   It is a great job and I hope I don't sound harsh... Hope you'll read through my feedbacks and comments are welcomed~

-aphrodite123-