After a very brief course, you will be whisked into battle with the final boss, O2. This battle is fairly simple and straightforward for a final boss fight. You will be flying around and have the ability to shoot crystal shards at him. To get started, shoot at his one eye and keep evading his shots until he flinches from the pain. While he's doing this, he will direct his halo towards you. Shoot it and it will turn different colors, finally disappearing altogether. After a certain amount of time, though, he will turn back to face you, but the halo will remain the same color. After it disappears, a vine-like tail will sprout from him and shoot out green clouds of gas. These cannot be destroyed with your gun as his normal shots can, so avoid them altogether. Do enough damage to the vine, and you will finally hurt him. After some time, he will return to his normal state, firing at you with his eye. Keep repeating this process until you defeat him.