I’m just going to list a bunch of dramas and the characters from them and explain how they act. I can’t find characters that are similar to them in dramas so I need some help. 

Kim Min Joon from Mad Dog - a cunning con man that also shows a vulnerable side when he starts trusting the rest of the team. Hides behind a naive personality, and tricks the other characters, making a grand reveal when they figure he is not what he seems.

Park Bong Soo/Seo Jung Hoo from Healer - hides behind a naive and meek personality in order to stay close to the FL. Is actually a badass, though I would have liked a more grand reveal. 

Oh Ji Hyuk from The Good Detective - probably the odd one out but he does pull some minor cons despite being a detective. He’s a total badass though, easily beating up thugs and then smiling and acting shy to the secretary who heard the fight. He also DEADASS trips a criminal while the rest of his team was chasing after him. I’m so glad this drama is getting a second season with the same actor :)

The ML’s in Two Cops - They’re both badasses in their own right,  one an amazing fighter and cop, the other a skilled and smart con man. The duality is hilarious!

The ML in Lookout - I wish his character had a more grand reveal rather than the FL figuring it out herself, but it made more sense for the story that way. I love that he acts like a suck up even around his own teammates justto keep his revenge plot going at all times. A brilliant con, though I’m sad about the ending. :(

I think the general theme here is a badass character that also cons people. It can also be like Cha Min from Abyss during the board meeting scene, when he absolutely dismantles one of the board members while being a dork for the rest of the drama. It doesn’t have to be fighting badass, it can also be a intellectual badass, like the leads in Witch at Court. Bonus points if the drama has romance. Also only Korean dramas please! Thanks!

I think the one character that fits your description is Ming Tai from Cdrama The Disguiser. He  acts like a spoilt good for nothing maknae of a big wealthy family, which is a front since he is a a highly trained spy.

another is Chen Zai Tian from Taiwan drama Black and White. he acts like a happy go-lucky always goes for the easy way detective. but he is really badass.

For Korean dramas, maybe:

  • Seo Hwiyoung (past/Japanese Occupation reincarnation) from Chicago typewriter - he acts like a school drop out wealthy young master who's hobbies are drinking, writing novels and women; but he is actually the leader if the revolutionist that is fighting against Japanese colonizers.
  • Dalpo from Pinocchio - he acts like the town's fool but he is pretty smart
  • Han JungHyun from Undercover - he plays wholesome family guy but he is in fact an undercover agent