Alternative Character Interpretation: Tae-goo's past is mostly an enigma. Why did he leave Korea? Did he regret the things he did, or was he just putting on an image to throw off his enemies?
Ass Pull: Tae-goo's survival of the final shoot-out in the Korean version.
Chang-yi fits the mold of an ideal bad boy. He's dark, he's brooding, sexy and tortured. Which makes people gloss over the fact that he's a neurotic psychopath who brutally murders people.
Tae-goo gets this as well, for being so darn endearing.
Foe Yay Shipping: There's lots of fanart of Do-won/Chang-yi on Tumblr and DeviantArt.
There's a fair amount of Chang-yi/Tae-goo art on Twitter, mostly coming from Japan. Do-won/Tae-goo fanart exists but it's extremely rare.
Tear Jerker: The international ending is just depressing. The last we see of Man-gil, he's mortally wounded and lying in Tae-goo's arms. We get the impression that he's not going to make it.