male lead seems like a cute naive boy but actually he is not

Sort of in the ballpark:

• Healer - The ML is a talented man-for-hire. He's a strong fighter and good with technology, and he's also capable of pretending to be a timid and naive newbie in the FL's office. Since he's a loner he is actually innocent / naive in some ways. 
• Love in the Moonlight - The ML is crown prince. He is smart and a capable fighter, but pretends to be useless and only interested in frivolous things like banquets and dances because of court politics.
• Tempted - The ML is a spoiled and traumatized rich kid who plays twisted games with his friends. As part of a bet, he pretends to be a sweet guy with feelings for the FL in order to manipulate her into dating him. Although he's good at manipulating, I wouldn't really call him smart.