I just realize that this is Japanese manga... I am so slow...

It's not. The original is Manhwa. Korean manga. The translation however is done for the Japanese version. It says so in the Summary.

Oh, Thanks for the correction. I though a Japanese mangaka makes a korean-like digital manga, since the writing were in japanese and they talk about Tokyo university and miso soup. But I did have doubt since the drawing show korean type background and in the last chapter they use stainless chopstick and long spoon.