The KitKat counter isn't that big. It's a small counter/table showing about 10 different speciality/expensive kitkats, and they offer some samples. Other airport stores stock the regular bagged/boxed kitkats
You'll want the KitKat chocolatory store (in the city, not airport)
https://nestle.jp/brand/kit/inbound/...ory/store.html
https://insideosaka.com/kit-kat-chocolatory/