First, I think that this one shot is a nice one.  I actually thought that it is an angst story or something along those lines at first,  but then I found out that it's more like a crack fic.  I don't know if you intend to make it a crack fic or not, but I surely had a good laugh while reading this~

About the title, though "Oppa, are you okay?" is not a very eye-catching one, it is good enough for this story.  It is simple and it fits the story perfectly so the title is good.  The short description made the story sound mysterious yet exciting, so same as the title, simple and perfect.

Moving on to the plot, I don't think I have met any story like this before, so this story plot is orginal. 

I was surprised when I first scrolled down the page to take a brief look at the whole story.  I was like, what? So short?  But you are able to write the whole story clearly and expressively in such a short one shot, so the length doesn't really matter.  As I read the story, I also found the flow of it is great and there aren't much grammar or spelling mistakes.  

The ending is a bit unexpected.  From the title, I guess that the worst scenario would be Chanyeol cheating on Hani with another girl but then it turns out to be Chanyeol cheating on her with a guy...  I was shocked especially when I knew that Chanyeol is cheating with Kai, who is her brother, on Hani.   It caught me off guard and I'm sure my expression is the same as Hani's when I was reading the scene where the boys are on the bed together...  This plot twist totally made the whole story interesting but I am sad that Hani was heartbroken... :'(

Onto the details, I think that the scenes are alright.  The fluffy scenes are really cute and the scenes where Hani is revealing her thoughts about how weird Chanyeol has been these days, helped to build up the tension for the story.  You did well in portraying Hani feelings.  However, being the curious reader, I'll want to know what happens after this and the thoughts of Chanyeol, such as did Chanyeol take Hani on the date out of guilt?  

On the whole, I enjoyed reading this fic but seriously I can't imagine Kai and Chanyeol are gay... O.o  Anyways, you've done a great job.  I hope you find this review useful, comments are welcomed and I really hope that you will write a sequel to this one shot!   

-aphrodite123-