Title

The first that came to mind when I read your title was the capitalisation of it. I believe the 'n' in 'name' is meant to be capitalised so that your title will be 'His Name is Leo' - now, this is something you don't have to fret about as actually most authors here do forget about capitalising their titles for the first time. Anywho, besides your capitalisation, honestly I was a skeptical about the title. In a way, it did lure me in - it makes me think 'How is Leo important in the story?' and 'Who is the main character?' after seeing the word 'His'. However, from the title, one can see that Leo will play an important role in the story which may or may not give away the actual plot - but again, this makes me intrigued on why and how Leo is such a vital character.

Can I say the title is original? Honestly, I haven't read fanfictions with the same-ish title - but it's not something new or fresh that would catch my interest at first sight as if you just entered 'His name is ________' in the search bar, you could see there are other stories with the similar title. I can see why you chose the title though! It does have relevance to the text which I think is a good thing since nowadays I don't often see the relation with the title and the actual story.

Appearance [Foreword; Description; Poster (if any); Readability}

You don't have a poster so I can't really comment on that, though I'd suggest to try and order one! Often, you can grab someone's interest with a poster, and since your story has an angst and supernatural theme to it, the readers would be able to have a glimpse of what the plot might be. Also, the readers would find it easier to picture how the characters look like as they may or may not know VIXX nor how their members look like. Moreover, you included an OC as well, and it's quite hard to picture on how you want us to perceive her as well.

As for the readability, it's alright! The font size is readable and the paragraph spacing is fine as well. I have to point out that in the first chapter you used the '~' to split the paragraphs, however, in the later chapters, you discarded it - I suggest that you either remove it for the paragraph spacing to be consistent or include it to indicate that the paragraphs have been split. Why? At first, I thought it was randomly placed there are firstly, it wasn't exactly centre-aligned and also I didn't see it any in the later chapters so I thought you might have forgotten about it. 

Moving over to the foreword, they were just words from you which I have no trouble about since you included a brief summary in your description about your story. Now the description - I felt that you gave out a bit too much information on the story. From what I can see, the story is about Leo hence the title 'His name is Leo' and thus it sparks interests on why he's important. However, in the description, you more or less tell more information about him and what he really is, a half-demon and half-human. Now, the fact that you just basically told us why Leo is really different just defeats the purpose on reading the story - us the readers, would already know why Leo is different! So it won't be a surprise when the truth actually comes out! In a way, it's a bit contradicting as most readers would expect demons to have horns and tail and whatnot. But by mentioning some traits of Leo such as him liking sweets and being hungry, we'd be a be a bit surprised when reading that he's part demon - however, imagine revealing that later in the story, we'd be more surprised. I suggest you either discard that sentence off so that the readers wouldn't know how Leo is different, or you can hint at it!

Example: Oh, and he's part demon, part human.
Correction: Oh, but can I mention that he's partly human?
Correction #2: Oh, and he's completely human - partly.

It's the not the best, but you can see that I try and not mention the fact that he's part demon. Also, I'm being quite vague so then the readers can guess what else he could be. So to improve, I suggest you just edit the last sentence so that you won't exactly reveal Leo's character. Oh! And I spotted a small mistake in one of your sentences.

Example: He can't speak human language but he understood what I'm saying.
Correction: He can't speak the human language but he understands what I'm saying.
Correction #2: He doesn't speak the human language but he understands what I'm saying.

You mix up the two tenses [which I'm going to explain more later on] which confuses me as I thought you were writing in the past tense. This is what confused me as in the first part of the description, you wrote it in past tense, however later on you switched to the present. I suggest you choose one tense to keep it consistent, and this also applies to the story as there were times where the tenses were switched. Also you forget the word 'the' so the sentence sounded a bit awkward.

This is an area where you can improve a bit, as this is basically where you try to lure your readers in! It's true that the first impressions do count, and with a few teaks here and there, I'm sure more readers would want to read more of your story. Also, there's not that much to change as well besides the description and the paragraphs so it's nothing to fret about that much.

Plot & Originality

I have come across fictions where the main character had, more or less, had the heart to let someone into their house, so I can't really say yours was original. However, I do like to point out that I haven't read a lot of those stories, so I was wondering in which direction you were going to take your story in. So far, Aileen has found a few facts about Leo such as his weakness, and more importantly his name. But she's yet to discover who or what Leo really is. As mentioned, you already told us what Leo really is however at this point of the story I could sense a bit of action and drama. I read that there'd be a bit of violence [along with some fluff] but it's interesting to see how Aileen will come to Leo's identity. He can't exactly talk and saying his name already has him weak - as mentioned, this isn't the type of image you'd think of when someone says 'demon' so Aileen's reaction would definitely be a highlight. I'd like reinforce that Aileen knows