What kind of stuff will you apply your Japanese knowledge on when you learn more?
Hmm, I never really had a concrete reason to learn Japanese. I can't help it but here's a long story (sort of):
In 2007-08 I wanted to learn another language - I don't exactly know why but I speculate that I always admired people who could speak multiple languages, broke borders of 'race' or 'countries'; to add to this, I live in a country with 100s of languages and cultures, there's always a sense of division in the people's minds if someone's from another race/subculture. I didn't like that and/or I wanted to know more about other people but language tends to be a barrier.
So I picked German. I bought some learning CD which didn't help me out much, eventually got demotivated.
About a year later I started watching Bleach anime after a friend insisted. I saw the first 60 or so episodes with English audio and later my friend lent me 100 or so episodes of it, saving me from the trouble of downloading or streaming them in my abysmal internet connection (this was in 2009). Problem was that it was entirely in Japanese audio and English subtitles, I figured it's alright because it would at least save me from a lot of bandwidth issues, plus it was holidays from school(12th grade)

. As I chugged through 10 or so episodes of it, I realized I could just get a lot of listening practice of this language and have fun watching more anime making effective use of my time and bam! (however I had made up my mind that I won't go about starting another language until I finish/come close to finishing this).