From the review:
"Initially, Dream Trigger has the appearance of a shoot-’em-up: you control a ship of some sort, fighting enemies while narrowly avoiding a massive barrage of bullets. The thing about it, though, is that you don’t shoot back because this is actually more of a rhythm game. On the bottom screen, there is a grid of sorts on which blue squares continually appear. These squares represent the enemies who are hiding from you and thus can’t be seen on the top screen. What you have to do is tap the screen to place colored blips on the grid. As a rhythm bar sweeps across the screen, it will activate the blips, revealing any enemies that are within their radius. Once enemies are revealed, they will then appear on the top screen where you can attack them by holding down a shoulder button and ramming into them."