Title:
I like the title, it connects to the story and the description and is a title I haven't seen before which is a good thing as well. Though, I stared at it for awhile wondering if "The Glow in his Darkness" would sound better because for some reason the "Glowing" makes me think it sounds weird but I'm not even sure myself now. Either way, the title is good and relates to the story so that's a plus. I think the title can be fairly eye-catching as well since you don't see it around much as a title, so good thinking on the title.

Description/Foreword:
I feel like based off the description, it could get a little cliché. Mainly because plots like this do exist but you do put a bit of a twist with the girl being an idol, not a fan or just a 'regular' person on the street that happens to bump into the idol since most people don't make the girl an idol.

After reading the story, I'm curious to when the second part of the description will happen where Chanyeol's being interviewed. I'm guessing it's going to be after her debut (which should take awhile since debuting takes 4+ years sometimes, sometimes less) so I think the story is heading in a good direction. The description doesn't give anything away either so that's another plus.

Plot:
The plot was a lot different than I expected which is good, I like the way the story is headed because you took the time to actually develop characters and plot in general.

We get a good amount of background information on these characters and I think the conflict is quite clear here; Chanyeol's stuck in depression and it's affecting his career and such which is where, assumbly, the girl will come in eventually. If you keep the story in the direction it's headed, I think good can come from it.

I hope you don't try to rush her into idol life though and keep her as a trainee for awhile since training takes years most of the time but since they're in the same company, maybe they'll see each other and start talking or something of the sorts, who knows. As long as you don't rush to get them to meet, which you haven't done so far which is good, I think you're all set.

Writing Style/Flow:
There weren't many errors that I could spot but one part made me pause. It was: 'I really am psychic. I must be going mental’,
Did you mean 'I really am psycho'? Being psychic is being able to see into the future and all that jazz, I think being psycho is what you meant since psycho and mental go hand in hand.

Another thing was this: tyres screeching
I've never seen the word 'tires' spelled as tyres before, so I'm going to assume that was a typo. Not a big deal really but that stood out to me.

Besides that, there's not much here to say about grammar since it was fairly good. As for the flow, I think that's pretty good as well considering the fact that you seem to be taking your time to develop the plot which is good. They haven't met yet and I think the story is going at a very steady pace which is also good, keep that up. 

Characterization:
There's only three chapters so far so there's not much to really say here since I have a feeling that characters will grow as the story progresses but as of right now, I think the characterization is fairly good this time around. Chanyeol's obviously struggling with depression and it's affecting the way he performs and I know how depression is like and sometimes, it is pretty hard to get yourself out that hole. But that's where the girl comes in to help him recover from it so I'm interested to see how the characters develop over time since I can see them growing in this story.

Personal Enjoyment:
Sorry for the shorter review but there really wasn't much to critique since I think the story is headed in a really good direction so far. I think if you keep it up, as I said before, I think the story will have a good outcome. Keep developing the characters throughout the story and keep the plot steady and I think everything will be all set. Even though I'm no fan of OC fanfics, I can see potential in this one.