These small red beans are called Azuki (小豆) in Japan.
Dainagon (大納言) is a type of red beans that are from Hokkaido and they are slightly bigger than regular azuki beans.
You can find azuki beans from Japanese grocery stores or health food stores.
Recipes Using Azuki Beans
Anko (sweet red bean paste)
Zenzai (Oshiruko) – Red Bean Soup with Mochi
Sekihan (red bean rice)