Like this "little sister", it is the same. In fact, this main meaning is elder sister, which can be used not only for your own elder sister, but also for girls older than yourself. If you add a small one in front of your sister, wouldn't it sound very kind? Anyway, I think if someone calls me little sister, I will be very happy, feel very kind, and that person is also very nice. If I had to choose between my sister and my little sister, I would definitely choose the word little sister. How beautiful this little sister sounds. I think this is also the main reason why the name "Little Sister" is so popular.
Some catchwords are good and some words are bad. So when we want to try popular words, we should pay attention. It's best to use some good popular words, not some bad ones. After all, we should be civilized people anyway. Popular words like "little sister" are good, so, ah, they can be more popular.