I heard of Kana compared if not equated to YKK, for example implicitly in Halo's comments, and Impz's place. As it turns out, any attempts to link them is bollocks. First and foremost, Kana is porn, albeit soft and pleasant.

The spin Extrange wants to put on it is very transparent:

One point about this manga that everyone notice: It’s ecchii, with some sex scenes (but nothing very explicit or hardcore).

and

My Lovely Ghost Kana is in it’s essence a manga about love and hope.

The "some sex scenes" above must be a new euphemism for "complete chapters such as ch.3".

The charitable explanation is Extrange being in denial. I'm no expert in ecchi, but Japanese mangaka commonly blow a bit of romantic and/or philosophical smoke, to make things more interesting. For example, let's look at a well-known Azumanga doujin, the name of which I've forgotten, and so I usually call it "Osaka in Love". It has a few panels with Osaka acting upon her love confusion, and it's charming.

Nonetheless no sane person would ever claim that's anything other than a porn doujin. But Kana is exactly the same! In fact, I'm pretty certain there's more frames of characters having sex in it than in most doujishi I've seen (I like my fluff). Sure, Mrs. Tanaka draws carefully around the throbbing members, which is why Kana is soft porn, but still a porn. And YKK is not porn. Let's be honest about it.