I felt that the crime and all the serial killer thingy was not required at the first place but as I moved on I found it interesting!

Does the story need it? or should it focus only on Rom-Com like Weightlifting Fairy Kim Bok Joo? 

Anyway found this meme which was so logical LOL...


Without the serial kidnapper the cop wouldn't want to protect her, and without the blackmailer the CEO would not want her to protect him.  Without these two elements there is no need for her to be strong, no need for any of the characters to interact.  What could this story be without the crime element?
I agree with you that we need the blackmailer but I'm not so sure we need the kidnapper. Bong Soon and the CEO seem to get into enough trouble without the kidnapper and I could see them constantly at the police station explaining themselves in their quest to catch the blackmailer while the cop becomes overprotective because he sees the CEO turning Bong Soon into a 'bad' person.
Actually without the killer and blackmailer the story might be pretty bad.
I thought that there would be more to the blackmailing story. I feel as if got resolved too easily/quickly.
the drama actually does a good job of transitioning between the different genres. 
the kidnapper part is necessary for bong soon's character development and for her to learn how to use her strength to help those around her.

It needs it. Why? To show do bong soon's strong character. If there weren't anything like that then there would be no need for bong soon's strength.  Also it would be a simple romcom that would get boring so yeah, it's necessary.
i think that the crime and mystery category def adds a little spice into this drama. it is sure one spicy sausage
@Rawr, you may consider the blackmailing story as introduction: there had to be a reason why Min Hyuk would need bodyguard so it made sense as a plot. But dragging it too much, wouldn't be good for drama especially that they can now focus more on other plots: romance, truth behind BS powers and kidnapper.
Kidnapper is needed to give drama nice "serious" punch, plus to be the reasoning for BS character growth.
I think it can be argued both ways, it would fit better if the writing was a bit more solid. The kidnapping stuff in episodes 7 and 8, especially 7, felt like poorly cut in add-ons in the show.
Yes every hero needs a villain, Do Bong Soon is the hero here, and In Guk Doo would do nothing thru the entire show if there's no crime case to solve lol
I think it's necessary. It definitely adds a depth to it... I went in expecting it to be a light romcom like WLFKBJ but was super pleasantly surprised when we got the crime element. It's the catalyst for Bong Soon realizing she wants to embrace her powers and use them for good and truly help people... which I don't think would have been the case if there had just been the blackmailing story (which I definitely don't think is finished yet, I mean we're only have way through... it was all too simple). Also I think it gives Gook Du more purpose as a character so he has slightly more plot than just being a romantic second lead... but also it was the catalyst for him realizing his feeling for Bong Soon as well so.

I personally think they're doing a great job switching dramas. The kidnapper creeps me out in exactly the way a kidnapper storyline like this should. I'm interested to see where they take everything.
Can be argued on, but I personally feel that it was a good addition. The blackmailer is a need to me because it shows he needs a bodyguard because of the blackmailer, it'd be weird without it. The kidnapper isn't really a need in my opinion but it's a good add on. I like how the show is showing a side of crime and mystery instead of being all focused on being a comedy love triangle. Plus in the end it might lead to character growth xD
I like the kidnapper.  What I really like is that they put some thought into him and made him intelligent and a true nemesis instead of just some one dimensional character to further Do Bong Soon's growth.