To unlock songs faster, at the end of your play, when the credits are rolling, try to FULL COMBO the credits. As in, when the name gets to the top, press a button. If you full combo the song, it wll count as one extra song. Meaning you can get 6 songs a game in less time.
BTW: The song played in the credits is CANDY.
To easy unlock two songs, go into game mode, select "Heavy" and pick one of the hardest songs. And when you fail, you should see the "NEW!!" thing flashing next to "Information". Check it, and you unlocked "Celebrate" By JJ Company.
Next, go into an Oni Course, and fail that. (To pick an Oni course, when you select your difficulty, go all the way to the right, passed heavy, and you should hear the announcer say, "This Mode Is Difficult!!".) Go into that, and pick one. Now fail it. You should see NEW!! again next to Inforamtion. Check it, and you unlocked Gentle Stress.
On the d-pad, hold Left + Right + Start at the song selection menu.