"It's wise to build close to your heart"

Place various blockers and turrets in order to protect the space station's life source.

Use the heart crystal's life source to buy and upgrade towers.

Don't let the enemy ships reach the life source. Place towers strategically to slow down the enemy and defeat them before they reach the crystal heart.

Controls

Click a spot on the space station to bring up the purchase menu. Click a tower from that menu to place it in the selected spot.

Click a tower to bring up the upgrade or absorb menu. Click the upgrade icon  to upgrade the tower, or the absorb icon to destroy the tower and return its remaining life force to the crystal heart.

Towers cannot be placed in such a way that fully blocks a path to the crystal heart.

Press the ESC or P key to pause the game.