Honestly, I just think it's because our boy is so set on NOT being the one. Like, he's so quick to assume that the string attached to Hara won't connect to him, that (assuming he kept that mindset) he'd technically never be with him at that rate. Like, Kaoru could be standing in his own way and if he just accepted the possibility that the string would connect to him, it probably would. Basically Kaoru's won't attach to Hara until Kaoru mentally allows that possibility. Otherwise, true to the "current" fate, Hara's string would never attach because to some extent Kaoru is rejecting Hara... Hope that makes sense. But that's just a theory. ('A FUDANSHI THEORY, thanks for watching!!')
The problem is that Kaoru doesn't have a red string at all - he has no string to be able to connect to anyone. That's the price, sort of, for having his powers. He explains it to Hara in the first chapter I think?
But Hara does have a string - that's the issue for Kaoru. He would forever be watching Hara's unconnected string, always afraid that one day it would be connected to someone - and that someone could never be him. And Kaoru also doesn't want to get in the way of Hara someday finding his fated person and finding happiness with them (that's how Kaoru sees it). I'm guessing that Hara will try to get Kaoru to snip off his red string too, so he can never connect to anyone else. That's the solution I would come up with, if I was Hara.
I think peoples' theories about Kaoru just not being able to see his own string are really clever and probably (hopefully!) right - the next gen twin with the power might drop the bombshell when he gets home from the park
This is so fucking saddddddddd, and my heart is totally aching. But for sure this manga isn’t tagged with tragedy so..
Yeah like Nyxmeow said, Kaoru doesn't have a string. In Akai Ito No Shikkou Yuuyo they explain how the whole red string thing works and your red string will connect to you fated person when you first encounter them. You can't control your red string based on your feelings. Otherwise, the main character of Akai Ito No Shikkou Yuuyo wouldn't have had such a hard time accepting who his fated partner was because it wouldn't have connected to the other guy to begin.
Maybe he does have it but is unable to see it.. such as fortune tellers can't see their own future, etc.. hope so :p
But like someone else already said in the comments, if Kamisawa wasn't able to see his own string then Keiji (who btw could see his own string) should've been able to see Kamisawa's unconnected string when he met him but instead he also saw no string on Kamisawa. Plus, the power to see and cut strings has been there for generations so why wouldn't one of his older relatives like an uncle or a grandpa been able to see his string? And if it was the case that they had a string but you just couldn't see your own string then one of his ancestors should've found it out at some point when looking at one of his relatives.
He's SO FREAKIN CUTE!!! That smile just purifies me!!