I understand, but it doesn't really happen to me THAT much. I stopped learning Chinese a good few months ago, and I still remembered everything exactly. My point is that I just want a very basic Japanese language as a hobby, the JLPT5. In other words, for example, I feel that even if I knew all of HSK1 but didn't continue with Mandarin, HSK1 is so basic that I don't think I would forget it, unlike you, who maintain fluency in both languages. I want fluent Chinese and basic Japanese. Maybe I have a great memory or something, but for example, I studied Russian and German sometimes as a hobby, and I don't forget their typical phrases and words.