The Japanese Step-Chest is a furniture item in Nintendogs + Cats that can be bought from Modo Home in all versions for $800. It can be placed in one of the four corners of your home, and cats will sit on it.
In Toy Poodle & New Friends, it must be unlocked with 7,000 Owner Points or by playing 24 days.
In French Bulldog & New Friends, it must be unlocked with 2,600 Owner Points or by playing 13 days.
In Golden Retriever & New Friends, it is readily available.
3DS: "This traditional Japanese chest once doubled as a staircase."