E-105 Zeta is different than the other robots. To defeat him, you need to destroy the cannons around his "head". Just lock onto all of them and fire. When Zeta is defeated, you will have completed Hot Shelter. To get to the final battle, head to the large green area where the other characters fought Chaos 6. There, E-102 will immediately start the final fight with E-101 mk II. E-101 mk II can be rather difficult, but his pattern is easy to learn. When he fires missiles at you, and lock onto them and destroy them. Then dodge out of the way when he flies at you, and then shoot him in the back. Repeat that pattern (while dodging his laser blasts) and he will be defeated. When that is done, you will have completed E-102 Gamma’s adventure, but not the game! If you've beaten every character's quest, you'll unlock this bad boy.