1. Like the title :) 

The titular Louis from Shopping King Louie is basically like that. He's useless but he's such a sweet cinnamon roll :D

100 Days My Prince. ML doesn't start out useless, but is soon thrown into a situation where he's completely out of his element.

I second the recommendation for Shopping King Louie also. The romance is a little more "juvenile" (for lack of a better word) than some but it's very cute.

  • The Eternal Love - FL. Somehow she still manages to be likeable because she's spunky and makes the ML happy. 
  • Advance Bravely - It's not that Xia Yao isn't good at anything. He just comes across as useless sometimes because Yuan Zong is amazing at everything. He mainly makes up for it by being cute, but also the things you mentioned too.
  • Tempted - ML is rich. Apart from that, I don't recall him having any talents or ambition, but he's loyal and devoted to the people he cares about.

Liar Game - The FL is not very useful but she trusts everyone and is very honest and kind.

Check out:

  • Take My Brother Away
  • Fool's Love
  • Please Love the Useless me
  • King 2 Hearts
  • Maybe
    • Takane No Hana
    • Strongest Delivery Man
    • Fight My Way
    • Mad For Each Other