Line is very popular on Taiwan, in fact it's the dominant app. All the locals use it, as well as Line Pay, and most companies have their website and services linked to Line. If you don't have Line in Taiwan, you're pretty much doomed to connect with friends unless they use FB Messenger.
Little Twin Star was something I liked since I was a little girl, I guess it's a way of holding to the childhood times, which often seems to be the best.
What's your favourite character? Comon!!! You must have one!! As you say, you been in Asia for so long 😃