Jungle Fish 2 (2010)

You might like this one aswell, this one isnt really as thrillery as this but the friendships and the mood are very similar.
The story is a girl dies and her classmates start to find out the truth behind what happend and at the same time you see how each and every charater develops.

Both dramas deal with problems arising from korean high school system, which affects the lives of high school students and with the difficulties on the edge of childhood and maturity.

A beautiful high school student, who is the top student of her class, mysteriously dies. Six of her friends who graduated from the same elementary school attempts to track down the reasons for her death by communicating in real time. While the six friends dig for the truth behind her death, they face difficulties in their studies, dropping out of school, bullying and boyfriend troubles.
Both about VIP students!
Both about suicide!
Both about corruption in school!

similarities: a student dies. as the story revolves, we get a glimpse of the korean education system and its insane competition and corruption.

Both have similar themes dealing with bullying and other matters that take place in an high school environment.

These two dramas give off very similar vibes. They are both on the more serious side, plot-focused with an actual lesson to learn from.
Whenever I think of one, I automatically think of the other.

Jungle Fish 2 (which is not really related to Jungle Fish 1, so you can watch it by itself) is about a girl who has died, and her group of friends try to find out why. It reveals a lot of hidden secrets about the school they go to, and about how many flaws there are the school system.

White Christmas is also focused on a group of people who are working together to try to get out of a horrible situation (It's hard to explain without spoilers). The students in both of these dramas face different but similar problems, and have similar yet different back-stories of their own.

I highly recommend watching both of these!