Normally you earn this when one of your characters reaches level 50 (you earn experience by collecting those red gems that fall from damaged enemies), however, this trophy unlocked for me while in the beginning of the first stage while playing as a level 0 Frau.
I'm honestly not sure what caused it to pop in my case, but I'll try to explain my progress so someone can test it later:
- I bought both DLC character packs (not the music though)
- I started an arcade stage as Frau previously to pop a trophy but did not level up in that instance.
- Frau had no leveling progress and the highest progress I'd made with any of the regular characters was to level 8.
- The trophy popped in the middle of the first section of the first stage.
I'm thinking this is a glitch caused by the DLC packs or something.