I finally understand what Ayane's KK2K is specified for, finally figured this string out. KK2K is usually (or rather has always been) looked at as some mashy string with no real use because of a slow low follow up. In the eyes of most (and I was one of them until now), this does seem extremely useless and even gimmicky. It is not, however. Infact, it's almost amazing how potent Ayane's KK2K really is, and after further testing last night and tested multiple set ups in matches earlier today, I can confirm that KK2K is indeed very potent.
And here's why; KK2K's purpose is for mixing up in the critical stun threshold.
K as we already know, is a very potent multi-purpose tool. It's an i12 frame tracking high with 27 damage, great range allows it to be used as both a keep out tool and a way to carefully poke while moving forward. It's also +2 on neutral hit and +25 in threshold and counter hit.
KK is strong for threshold mix up and even as a starter for threshold. KK's critical stun is so good that it leaves Ayane with +27, and +18 advantage even at fastest stagger escape, so it causes a must-hold situation because you cannot block follow ups of i10 to i16 frames at all.
Now add the 2K low follow up into this, and what you have now is a stun launch+tracking low guard break mix up in threshold. The delay window into KKK and KK2K is so huge, that you can literally mix up off delaying the 2K low with high/mid launches and high/mid strikes the same way, visually. You can delay KK2K up to 64 frames, but you want between 44 and 60 frames, ideally. 44 is without delaying into the 2K low.
Not only does this work with just normal KK threshold mix ups, this is even more deadly with the 64H+P throw mix ups and even the 64H hold mix ups. No one is used to seeing the 2K low this way, or at all (let's be honest). Another great thing about KK2K is that against players that have no intention guessing the must-hold situation, wait the stun out and mash, the 2K low will counter hit them regardless if they try. Not even an i9 frame jab can counter hit this. So KK2K does not lose to mashing and you don't lose any pressure.
If the 2K low is blocked, you're at +19 and you get a guaranteed BT6P for launch (BT6P > 6K2K) into okizeme. You also have 3 distance safe tracking moves while in BT stance, 1) BT K -12 (it is -13 but if blocked at a distance, it's -12 and cannot be thrown at all), 2) BT6K for +1 at range (requires a microdash in BT stance), 3) and BT2K at -11 (requires a tiny microdash in BT stance so BT2K can hit or be blocked, distance safe). Free canceling after the 2K low and doing 3H+K also works wonders here.
If the 2K low hits, then you get okizeme. You're at +27 if they decide to tech up, if they don't tech up immediately then you have 1P/1P2K, BT2P and BT2K to force them up.
There is tons of mix up potential here, all of this applies to the 1H+K low as well. I love this string now.