Before launch, Capcom revealed that Monster Hunter Diary Poka-Poka Airou Village DX (which came out on September 10th in Japan) would get a special collaboration with the Animal Crossing series. To be more precise, the collaboration is a special Tom Nook costume for your Felyne, and it’s now available!
However, to get it, you first need to complete a special quest. But in order to unlock it, you first need to become friends with the Postman and the expedition quests receptionist (the one with the blue hat).
Here’s some screenshots for the Tom Nook costume: