Title:
The title is very fitting as bubbles are the reason they all seemed to meet and the last line brings up the bubbles again. I wouldn't say it's the most exciting title but it's definitely very fitting and appropriate for the story which is great either way.

Description/Foreword:
I wasn't expecting the fancy layouts, that's for sure. Anyways, the description is really just an explanation of what the term bubbles is so there's not much wrong with the description except for one small thing.

You wrote: "when we were eight year old"
Technically, it should be: "when we were eight years old"

The foreword doesn't reveal anything that's in the story, which is good, and it makes you wonder what the person is referencing to when they ask if this is a punishment. So, it does make the reader think a little bit which is also good.

Plot:
I like how at the end, Jiyong says he is texting Seunghyun despite the accident happening. But overall, the plot was bittersweet but it seemed planned out very well. It starts off quite happy and sweet, the accident happens and everything goes downhill, and then at the end it ends fairly sweet with a hint of bitterness. It's a pretty short little story but it gets the point across and doesn't drag on which a lot of stories tend to do these days.

Writing Style/Flow:
I did catch a few grammatical errors, nothing major.

But one sentence caught my eye in the 'ACCIDENT' section. 
It says: "What for he apologized for?"
I think you meant: "What did he apologize for?" 

In the 'REMEMBER' section, there's a missing word in one of the sentences.
"We should do it after succeeded in job hunting."
I would add the word 'we've'. "We should do it after we've succeeded in job hunting."

Besides this, the story was very easy to follow and the flow fit. The story was well thought out and written quite well. I think you did a good job despite the minor mistakes.

Characterization:
Jiyong's characer at the end really gives a sense of realism because sometimes, people who lose a family member/loved one get delusional at times and think they've never left. So I liked his character.

Dara's character is hard to really pinpoint, which is fine since it is fairly short, but you do get a few different emotions from her in the story which is good. She's a pretty good character overall. 

Personal Enjoyment:
Short, simple, and bittersweet - I enjoyed it. It was written well and wasn't confusing. I saw that it entered a writing contest, so good luck with that and I hope it gets something since it's quite good. 

I hope this review helped and if you got any questions, let me know. Since the story was kind of short, it was harder to do a longer review so my apologies on that but I hope I got everything I wanted to say across.