Omg, I love those stories .
In modern k-drama, the first I thought was : the healer . The ML pretends to be a weak journalist but he is actually super badass . And other one , I was thinking but I see you're watching is Alchemy of Soul .
In c-drama, "the untamed" , a guy who was super strong before, died and came back to life in a weak body . So everyone thing is weak but he actually badass too .
Word of honor , is one of the best C-drama I saw . The two main lead are super strong and both hide their identities . One of the ML pretend to be a weak poor guy .
I can't find other one right now , but If I remember something I will write it . I hope I could help you a little.