I wonder if the omake are just "chapters without assassinations" 🤔
And as for the detective being creepy or not, if this wasn't a gag comic where the MC kills a one-dimensional Shitty Person every chapter, then the detective would be a shithead. But it is a gag comic, so it's okay to just go along with how the author shows them. The detective is like a big dumb dog who knocks people to the ground on accident because he's so excited, and Kanako is someone carrying a fragile vase. She's not nervous because she doesn't like his attention as a person, she's nervous because he's a detective and she illegally kills people