Battle. There's only one normal battle theme, but it is so catchy we probably don't need others.
It's Easy, So It Sucks!: The main criticism of the game is, despite only having two party members, it is overall quite easy. In particular leveling up in this game gives you incredibly potent stat increases, decreasing grinding but also making it really easy to become stronger than most bosses by accident.
There's only one normal battle theme, but it is so catchy we probably don't need others.