The Heirs
I present you The Heirs, which I consider the best tv show ever. The Heirs has the most beautiful ending you can think of. This is not a new quality in the genre, but Kang Shin Hyo almost never goes below a certain level, which is clearly confirmed by this tv series. I think it was worth seeing such a brilliant but sad story. It's taken me multiple rewatches and a lot of hours on the wikipedia so I finally understood everything. The sum of detail and small things of the tv show that you can long time later is really amazing.
Storyline of The Heirs
The series follows a group of rich, privileged, and elite high school students as they are groomed to take over their families' business empires. Kim Tan is a handsome and wealthy heir to a large Korean conglomerate who is sent to study abroad in the U.S. But in reality, it's a form of exile, as his elder half-brother back home, Kim Won schemes to take over the family business.