Previous note: This review may look somehow harsh, but it only aims at giving tips for the writer to improve. Lies don't do any good at all, so please be understanding^^

Username: leejiwoon_18
Story Title (&link): Too Innocent? I Don't Think So
Main Characters: Exo K, Exo M, OC, Bobby(ikon)~ (+parings): Kai & OC- Jiyoon (Lara)
Genres: Slight angst, gangs.
Current Length: 3 chapters~ completed.
Rated? No.
Reviewer: MaRwAaa.
 

Title: Although I usually don't prefer the long titles, I liked yours very much. It is so expressing and simple. And it also makes the reader curious...who is not really innocent? Why? And how? This is nice, and it also gives me a hint about the story's genre. Well done!

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Poster/ Background: Your poster was made really well. The pictures of your main characters were chosen accurately, too. The expressions of the OC which looks very innocent but not-really-so is really good. Kai's expressions are meant to be here. I like the colors of it; not so dark...not so light, which is perfect for the opposition of your story's two ideas(innocent & not really innocent). The quote over there is the best addition to it. I am totally in love with this saying "Don't judge a book by it's cover." Good job!
The background is well done, too. The same is said about it, but to be honest, I would prefer it to be empty. I feel that it sometimes may distract the reader attention. A blank background with one color may do better here. 

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Description & Foreword: Despite of the numerous mistakes of your foreword, I liked it. It really could convey me the content of the story without revealing much of it. I particularly liked including the two quotes of the two main characters. They could give me the feel that I am going to read some good story with a good writing style. However, I didn't expect much due to the weak English you have there. Even in the foreword, which must be the beautiful and attractive door to your story, your writing didn't impress me with the amount of grammar and spelling mistakes. Sorry! But this is the truth~

Creativity/ Originality: I do admit that your topic is somehow creative; I haven't seen something like it before. This makes a good point for you. It's really great when you have a different idea, and that what made your story good to read. 

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Plot: A totally mess! Really sorry, but this what I can say about it. It needs a lot of improvement. You need to complete some open points and draw some points bigger. There are many points where I wondered "Why?", "Who?", "How?", and I got no answers even after I finished the story. I will mention some of them for you:
1. Why did her heart stop beating when she knew that he is cheating on her? Does she love him that much? You didn't show us that. I couldn't see any evidence that she is in deep love with him that she got really shocked and sad when she knew about his real self- being in a relationship with another girl.
2. " It's not that I'm looking for her but it just feels so weird. It's like she know something and I don't." That was Kai who said it, but really...why it would be so? If my friend didn't message me for once- although she everyday does- does that mean that she knew something I don't know about? She may be so busy or may be sick. Don't fool your readers; try to show them the most logical ideas and events. The more it gets real, the more it attracts and satisfies them.
3. "She didn't tell me a lot, but she tells me that she is close with 13 guys and 3 girls which surprise me." This was also said by Kai about Jiyoon. Now, I have to say that adding the numbers is so awkward. Why would she tell him the exact number? and why would he repeat it? It should be something like this>" She didn't tell me a lot, but she told me that she is close with a number of boys and girls, which surprised me." So you don't need to put their number to tell us that she's a part of that known gang of 13 boys and 3 girls.
A good point: putting the two quotes, which you included in the foreword, in their perfect places in the plot is something amazing and attractive. I totally fell in love with this work of yours. 
I am talking about these two:
"Just wait and see, Kim Jongin. Me? Too innocent? I don't think so." She whispered each word making me gulp my saliva. Then she walk away like nothing happen.

She never said she can't dance, In fact; she didn't do y dance.
She never said she can't sing, In fact; She raps.
She never said that she was the innocent one, In fact; I was the innocent one here.
It's like what they said, don't judge a book by it's cover.

In general, the plot you have needs a lot of points to be checked and others to be added. I advise you to make it a one shot, add some descriptions here and there, make connection between the events, and make some development of the action. This will improve your story quite a lot, and it will make it more professional and pleasing to read and review. This is my advice, and it's your own story, so choose what you find to be good.

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Spelling, Vocab, and Grammar: I won't say much on this section, because I've said it before. Your English is very weak, and you have errors and mistakes in every line. This makes your story really low-graded. Therefore, my advice here is...ask a beta reader to proofread your story. You totally need that~

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Characterization: Your characters are so many; a very short story doesn't require that huge number of characters. And even if they have to exist there as 'gangs' or whatever, don't mention them in your foreword>(I actually forgot to tell you this in the foreword section, but here it is, anyway). Please, if you like Exo as a group, don't try to drag them all in your story; you can make a story for each one of them...lol^^ I like them, too, so I would be happy to read that^^
Another thing is...I could neither understand your characters nor feel them. You didn't allow the reader to go inside their thoughts or feelings that much. You didn't allow them to persuade us of their actions, which seemed really weird sometimes. For example, in the final chapter, when Jiyoon sang a song in the club meaning to convey a hidden message to Kai; why did she do that? Did she want to take revenge? To show him that she is more than what he is worth? To make him regret his actions? 
Moreover, when he grabbed her hand and dragged her out... why did he do it? Was he jealous? angry? curious? or was he really in love with her? I couldn't understand anything here. 
Remember...you cannot leave the reader curious and give him no answers.

Flow: It was really awful. The events happened so quickly that I couldn't realize it. Even for a one shot, your story's flow was not made well at all. You need to fix so much things in here. Draw some new events to transfer your readers smoothly from one important point to another. Show us the story as a story... not like a group of events that are barely related to each other.

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Writing Style: Not the best. I particularly hated the change of the narrator. Why did you do that? If you want to tell us about all the characters and about what thoughts they have and how they feel, then just use the third person narrator, which is almost always the writer(You).
Another thing>> look at this:
"You're too innocent for him, Lara. Don't you hear it from the whole school?" Baekhyun Oppa continued. "Wait, I thought that was only because of them are jealous of me that I get to be with Jongin." "Unfortunately it's true Lara."

Now can you tell me who said what? You are the writer, so you will probably answer it easily. But you are writing this story for people to read it. Readers are not always happy to go on analyzing who said what. You have to make it clear for them. This kind of writing may disturb the reader and make him or her draw back. Honestly, if I was reading your story and not reviewing it, I will certainly quit reading it as I am so lazy to analyze things which you are the one who are supposed to make it clear for me.
 

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Extra & Notes:
I think that you only need some important improvements for your story to make it better. I liked the idea of your story, and I felt really sorry that you didn't draw it in a good way. Sorry for being somehow harsh, but as I mentioned before, I just try to give you tips to improve your writing^^ And this review is based on my own opinion and experience.

Thanks a lot, and keep up~