The game is focused around Naija and her journey, much like Metroid and Symphony of the Night focus around Samus and Alucard. That said, there are other characters that factor into the storyline, but how many and to what extent I don't want to talk about yet, as I don't want to spoil anything.
There's also a diverse range of interaction with creatures, some are hostile, some are friendly... many have unique ways of interacting with Naija, with varying effects. There's also a few other gameplay elements we haven't revealed yet.
You learn songs in different ways as you progress through the game. The menu left side of the menu has a list of songs, the right side plays the notes for you when you hover over one of the song icons. Clicking a song icon has Naija explain what it does.