Zegapain (2006)

Sogoru Kyo is a normal high school student with great passion for the things he holds dear. In fact, his love for swimming is so great he is attempting to single-handedly keep the team alive. However, his life takes an unexpected twist when meets a strange girl at the pool whose existence shows him an enemy force that is threatening the very existence of humanity. These beings known as GARDS-OMS seek to eliminate humanity and take Earth for their own. His choice is to live as he has been, or take a place in the cockpit of a mecha to stop the extinction of humanity. They often say the truth will set you free, but in this case the truth may destroy Kyo and leave his beloved hometown without the hero it so desperately needs.