One of the Japanese winter fruits is oranges. In English it is “satsuma” or “mandarin orange”. But neither English can communicate in Japan. Japanese think of sweet potato from satsuma. There is no familiarity with the word mandarin orange.
Mikan is smaller than orange and sweeter. Even a child can easily peel off with their fingers, because its skin is thin. And most mandarins do not have seeds, so you can eat whole but the outer skin.
However, when you eat a lot of mikan, your hand gets yellow. It is the work of pigment called carotenoid contained in mikan.