... so disappointed, what should I do? Should I get Japanese citizenship?

I don't know why you are disappointed because nationality is very important. Be cautious. Maybe you are fine in Japan and think that Japan is suitable for you. You should also consider the opinions of other relatives and friends in China. It is inevitable that one can't stay in one place and not return to the motherland. At that time, other relatives and friends thought you were envious or something else. If it is other countries, I think there is no big problem. More and more immigrants can choose from Japan. Otherwise, you will regret that even if the nationality is returned.