A good writing, a personality, and having something about them that makes them admirable in some way. Even if they don't go through the most changes, there should be at least SOMETHING in there that can grab the audience. Whether or not they go through change, or if they're just fun in their own way.

This is why characters like Takaharu, Lucky, Tagiru, and Sougo don't work. They're basically those characters, but without any of those things, and instead being replaced with traits that make them insufferable and flat out unlikable.