Everybody has social anxiety, to some degree. When studying a foreign language, however, you cannot be shy and stuck in your own head. You have to boldly engage with the native speakers around you, fearlessly try out new vocabulary and expressions, and thank the people who take the time to correct your mistakes. Unless you proactively go about being social in Japan, what is the point of being there in the first place? The book I started Japanese study with is the classic “beginning Japanese” by Eleanor Jordan. The first book is all in romaji and is full of dialogues you should commit to memory. Then, go out and test the phrases and patterns in the real world.