Nothing will be sugarcoated in this review, please keep this in mind. This is to help you, not hurt you so please keep that in mind as well. I think I sound a bit harsh but I don't mean to sound that way, it's just hard to tell with typing.

Title (5/5):
At first glance, I was fairly interested in the title considering Angel's aren't the ones to wear masks. I feel like when we think of 'masks', we connect them to bad things. A good example would be in a game called Yandere Simulator, where you can join the drama club and wear masks to murder people without your identity being known or even Block B in Very Good, where they're all wearing masks to rob the bank. So I feel like, in a sense, the mention of masks are related to more bad things compared to good so I thought that was interesting. The title is probably talking about one of the female characters, I'm going to assume it's the main character (or the one that has the most scenes) but who knows. I'd say it's a pretty eye-catching title regardless.

Description/Foreword (5/10):
Starting off with the description, there were some weird wordings in the description but I'll be putting that in the writing style section since that's where grammar related things go. Anyways, judging by the description (and... the foreword) the OC is quite determined in a sense and that could make the story interesting.

The one thing that I didn't like about the description is the pictures. I always. always, always, say this in any review for a story that puts pictures in and I'll continue to say it: books don't ever give you pictures of their characters because you're supposed to be able to describe them in the story with your words by introducing them when the time is right (the main character is the first to be described usually). They're introduced with detail and sometimes, when people put in pictures on AFF, I feel like the descriptions of things aren't going to be at their bests but we shall see about it when it's time to start reading.

Another thing is the change of POV when the part after the pictures comes up. It starts off in third point of view with the description and then changes to first point of view. The story seems to be in third point of view so everything else should be as well, this includes the foreword. It shouldn't be changing point of views.

And finally, the author's note. The type of OC you explained as cliché isn't the only cliché kind of character out there despite it being the most overused character in the ballpark. The one you described is also quite cliché (maybe not as cliché but I'd say it's close enough), just from what I'm reading - I haven't started actually reading yet but the description and foreword are first impressions, for several reasons. I have seen this kind of female OC plenty of times, even in stories I have previously reviewed years back so, to me, this isn't that new at all. There are a lot of y, mean, selfish, and whatever else is listed, OC female leads and if not written correctly, they may be seen as annoying; I'm hoping this isn't the case here.

After reading the story, the Author's note is inaccurate. You forgot to mention that she was a bratty child who is a lowlife that is also cliché. You successfully made her my enemy but that's not good for a story, you're not supposed to hate the character that's going to be the person you see all the time since it's mainly in her point of view. That's not going to make people want to stay and read, it surely didn't make me want to. I don't want to read a story where all I do is hate on the main character because she's acting like a five year old who can't move on and realize that the person she wants is happy with who they're dating. A character having flaws, not being innocent, and being a y brat doesn't make them not cliché.

*Plot (15/40):
I think there's a few problems with the plot and I think I explained most of it while talking about Ami's character as a whole but I'll delve into it here since it's more than just the characters. The plot's conflict (from what I'm getting): Ami loves Sehun but acts like a childish brat to try and get what she wants which is, of course, Sehun.

This is the plot I've gotten from reading and I think this isn't a strong plot because of several other reasons. 

1. Ami's character. I'm not going to talk about it here but her character is quite the turn off. When you said she was going to be selfish and be a , I expected something completely different; here, she's really just a spoiled brat with a bad attitude if anything.

2.  There's no plot twists really, I don't feel like there's anything really exciting going on. I feel like I can predict some things that are happening and for some reason, I feel like Luhan's purpose is to 'seduce' or 'steal' Eunji away from Sehun so the brat can try to have him despite the fact that this plot would be the worst cliché you can get. I don't think this is where it's headed but it's one prediction I had.

3. The events happening don't seem to make sense and/or are not logical. Example: Ami trying to kill herself. Suicide isn't to be taken lightly and for her to try and kill herself... for pretty much no reason is pathetic. She's heartbroken, sure, but that's not a reason to kill yourself, I feel like this is one of the times where she just wanted to get attention which is a no-no. I was literally sitting there with a 'what the ' expression while reading this because suicide does NOT fit in this type of story. I talk about this more while talking about Ami as a character.

4. I feel like everything is scattered. I feel as if some events or chapters are kind of "fillers" to get the story moving which isn't always a bad thing, there's always going to be fillers, but I don't really see the story progressing forward much. There's been little to no progress made from the beginning of the story I feel like and I feel like some events should have not happened (such as the suicide, that was highly unnecessary..).

5. As I said before, I feel like the plot isn't moving forward. The conflict is very obvious, as I said before, but there's nothing really happening besides making Sehun feel bad because Ami is a prick and a lowlife. I feel like you're trying to make people feel bad for Ami at some parts, maybe it's just me, but if that's the case - she doesn't deserve it. Anyways, I don't know what the plans for this are in the future but as of right now, I feel like much hasn't happened to actually progress.

6. Who has in a hospital? I'm.. what. This is another example of a scene that's just.. unrealistic and not needed. Considering how much blood Ami must have loss, I don't think she'd even have the energy to move let alone have . I don't see how this event furthers the plot either, it's more like a filler event as I said before. It does nothing to really progress anything.

Either way, moving on, there's a lot I'm unsure of with this plot. Especially with some of the events going on here. Maybe I tend to look into reality too much (or being logical for that matter) but I just... this story isn't going anywhere for me. I feel like it's still at square one and I don't know how long this story will drag on for. I think it needs a real event to push it forward, not one that's a scene or Ami being a dumb kid. The here just kind of seems like PWP ( without plot) right now since it comes randomly and out of no where.

The only advice I can really give when writing is to plan everything out on paper, that's usually what I do when writing a fanfic that I want to have good meaning to it or an impactful story (the other ones I just Yolo and end up hating). Timelines help too, I know it's extra work but I help improves stories by a lot I like to think.

*Writing Style/Flow (10/20):
As I said before, there's some weird things going on in the description and such that I had to do a bit of a double take on (whether it's because I'm tired or not, I don't know but there are a few awkward things). 

1. Tricks and acts were her games, prays and fate never existed in her dictionary of life.
> The word 'prays' doesn't sound correct in this sentence. To correct it, since this is what I think you were going for, you'd use 'prayers' since prays doesn't make sense in this sentence.
Fixed: Tricks and acts were her games, prayer and fate never existed in her dictionary of life.

2. No matter what is waiting ahead, she doesn't afraid to bear the sins.
> The word 'doesn't' is the problem here. It literally says "She does not afraid" which is not correct and you wouldn't hear someone saying that. You would use 'Isn't' because she is not afraid to bear the sins. 
Fixed: No matter what is waiting ahead, she isn't afraid to bear the sins.

3. Or maybe, I dislike the fact how cruel the authors did to the second leads and also the bltches in the stories.
> First of all, like I said before, this section shouldn't be in first point of view since switch point of views from third to first is a no-no. Second of all, the word es seems to be spelled with an 'L' instead of an 'I'. But the sentence doesn't really make sense because of the "I dislike the fact how cruel the authors", not only that but I wouldn't call the characters "es" since.. I don't know, I don't think they were really es. Either way, I fixed the sentence to make more sense.
Fixed: Or maybe, I dislike how curel the authors were to the second leads and also the es of the stories.

4. Chapter 5:
"You're shameless don't you?"
> This makes no sense in the context it was used in. It's literally: You are shameless do not you?" which... just makes no sense. Also, there should be a comma after the word shameless. Instead of don't, it'd be aren't. 
Fixed: "You're shameless, aren't you?"

5. Improper grammar.
If I really did see that correctly, did Jongin say "Da fug"? This is a story, not a text message range. Works of fiction, even if they are fanfiction, are supposed to be written with proper grammar, not slang that no one uses anymore. If anything, it would be "The " as that is proper and... Da fug sounds very childish.

The flow is a bit scattered to me, one moment Ami's being a brat and trying to.. prove some point by being a head to Sehun and then she's found almost dead in a bathtub. What? I don't know anymore, I'm just kind of... puzzled at this.

*Characterization (4/20):
For characters, let's start with the main one.

By chapter two, I have a dislike for Ami. She seems like a brat who is only mad because she can't have what she wants which is Sehun. The way she acts is like a child at some points and I think that's just annoying especially when she said "He said he's not going to give me what I want. Because he already has her." Does this not sound bratty to you? I think Ami falls right into the cliché character list because I've seen characters like this one before and her attitude is enough to make me want to leave. Reading chapter five further proves how much of a spoiled y brat she is which isn't a good character, you don't really want the main character to piss you off to the point where you don't want to read the story - that's, personally, how I felt and I didn't finish reading the story because I can't stand her. I absolutely hate people like Ami, especially in real life, so she's not a good character for me and I don't think I can tolerate her. Like: "I don't want anything from you unless you leave your girlfriend." So, in other words, Ami wants him to be miserable because she's a jealous little girl that can't grow up? Nice. Then she tries to kill herself just because she wants to... prove a point or what? She's obviously not suicidal and shows zero sign of depression so what the hell? Trying to commit suicide for the reason she did is, in all truth, quite pathetic and this kind of shows the problems with her character.

There's a difference between being selfish and mean and being a childish brat on purpose because they can't get what they want. Ami is a childish brat who is mad because she can't get what she wants and wants to make the person she so-called 'loves', be miserable. Also, if she loves him as much as she claims why would she even allow Luhan to touch her? If she really loved him, despite being oh-so 'heartbroken', she probably wouldn't have let him.

There's something seriously wrong with her, and yes I'm going back to the suicide thing because this is a problem, because she tried to kill herself over a boy, for one. Two, it's like she WANTS Sehun to suffer and blame himself if she did die which is the worst thing you could possibly do to someone since it could put him into depression and HE could take his own life. Yeah, she's selfish and a  in this aspect but as someone who actually wanted to commit suicide when I had depression years back, this is just purely upsetting. Ami's a lowlife. Disliked her from chapter two, hated her from chapter five forward.

Moving on to someone else before I go on a rant, let's go to Luhan. Typical playboy, not really impressed with his character mainly for the reason that he's always put in as a playboy, I've seen it in a lot of EXO fanfics by now and it's like a stigma he has surrounding him. I don't really see his point in the story but I think I had a pretty good idea since he's probably going to be used in a plan to sabotage the relationship and all that. Maybe he also has feelings for Ami, I don't know anymore since everything is slightly scattered.

Eunji I can't talk much about since she doesn't really show up enough to talk about her. And Sehun, I feel bad for him and I'm wondering why someone would keep Ami around, best friend or not. Ami is a spoiled brat and if I were Sehun, I'd block her from my life. She's a ball of drama and brattiness and Sehun's happy with Eunji so I don't understand why she's being a jealous child. He's a caring person and so far, I think he and Eunji are the only people who don't make me want to turn my head. Luhan's just whatever since he's just a support character really but Ami is no no.

Overall, I think the characters are lacking a bit. Maybe try to develop Sehun a little more too, I feel like we know little about his character. I don't think there's much you can do to give justice to a character like Ami.

Personal Enjoyment (0/5):
I won't lie and say I enjoyed it because I don't think I did. First of all, Ami is just as cliché as a lot of other OCs, maybe not the ones you were targetting but yeah, she's not unique or special. She's a brat and I don't like her character at all. The plot isn't getting anywhere, in my opinion, and I don't really see how this is going to end because it just doesn't seem to be getting anywhere. The grammar wasn't a problem in reading since I could understand everything but the plot and characters kind of lack to me.

The suicide thing was a horrible turn off and I don't see why it's even put in here. I'm fine with darker stories involving self-harm and suicide but this? God no, you don't do what Ami did ever. This is not a story that should have this kind of stuff in it and suicide is a very sensitive topic to many people, so a warning should have been placed at the beginning of the chapter. Suicide because you can't get what you want is the most pathetic thing a character in a story could do and I don't condone behavior like hers.

Total (39/100):
I tried my best to explain why I gave the score I did within each section and I feel like I did come off as harsh at some points but the suicide thing did kind of tip me off. Her character, to me, is a problem and I don't understand why she's like that, I feel like her character needs to grow up a bit. I think the title is the strongest thing going for this story right now since that's a genuinely good title, I like it a lot. It's the characters and the plot that kind of hinder this. 

I know seeing a low grade is something no one wants, I wouldn't either but I don't want to give pity points. But it's fine, there's always going to be different opinions on things and this is mine, I tried not to sound harsh but I always fail since you can't tell how I'm talking by typing. I tried to point out what I could but I hope this helps anyways.

If you have any questions, you can ask me but I hope I explained everything here good enough (I'm bad at explaining, sorry) but if you do, I'm a pm/comment away. Please don't forget to pick up your review and credit the shop (rule 03). I hope this did help a bit and I'm sorry if I did come off as harsh, I am only trying to help.