But does this type of bullying happens in real life? I'm totally ignorant about this subje...

To be honest, it's rare, and most of the ruined not as obvious as this but I can give you an example of something that happened where I live.
There was a girl in a class, she wasn't really rich or anything and didn't wear makeup or cool clothes, so she was a bit of an outsider since the other girls thought that was all that mattered. Somehow, someone got an idea(I don't know the details) to make a blog, and in that blog they trashed her and made fun of her and such. The blog got a lot of views and because of how untechnological

(hit send before I was done )the police are in my area nobody really noticed or did anything about it, even when people told. Years later it became a huge deal though, and I think the girls had to post fines and such.

It's not really physical bullying and obvious like this, but it really hurts a person in the same way.

This type of bullying apparently happen in Japan which the kid will be too depressed and stress and will end suicide. This type of bullying is really..... i don't even know what to say. Damn fucking sucks you know.

This manhwa is based in South Korea and the author is Korean.
There are a lot of issues illustrated here that are actual problems in Korea. The two main are physical appearance and Bullying.

South Korea has the highest rate of plastic surgery. In South Korea you can be denied a job based on your appearance. Even if you graduate from a top university, if the company deems you ugly they reject your application or suggest you get plastic surgery in order to qualify for the job. Many parents even give their children, double eye lid surgery or nose jobs as graduation presents.

South Korea has the second highest suicide rates in the world.
One of the main reasons for suicide rates amongst children to teens have been because of bullying. School bullying is a big issue in South Korea, a top girl group was pretty much exiled from their industry when there was an alleged bullying rumor that they had bullied one of their members. Every year you see many report on the news that teens have committed suicide because of bullying.

If you're interested, you can just type "South Korea bullying" or "South Korea Plastic Surgery" on google and you'll get a ton of articles talking about this problem. There's documentaries on YouTube as well.

Thank you for all your replies, they were helpful