The game is supposed to be a premise to Smealum's DS homebrew Earth Invaders. If you haven't heard of it, no nedd to worry - the developer says that the gameplay of this PSP homebrew has nothing to do with the DS one.

While the DS Earth Invaders was a shoot 'em up, Earth Invaders o is an adventure beat 'em up.

Here's how you can control the very Goku-looking character:
- UP RIGHT LEFT: To move itself
- UP RIGHT LEFT (2times): Dash
- HIGH: Regenerate his ki (when one is not in flight)
- LOW: To defend itself or transport the enemy (if in a hurry at the right moment) (when one is not in flight)
- Stick: To move itself
- X'S: Jump; Fly
- O: Kick
- / : Fist blow
- Square: Ki blast (energy ball)
- R: uSpeed
- L: Reverse gravity (to walk to the ceiling)
- L+R: Leave