Zegapain

Kyou Sogoru is an ordinary high school student in Maihama City who loves swimming, gaming, and hanging out with his friends. His quiet life takes a sudden turn when Shizuno Misaki, a mysterious girl, asks him to jump into their school pool with her. The moment they leap, Kyou is pulled into a devastated world where humanity fights against the alien invaders called Gards-Orm using giant humanoid robots called Zegas. The resistance force Cerebrum leads the struggle to stop the Gards-Orm from wiping out mankind. As Kyou joins the battle, meets other Zega pilots, and sees the horrors of war, he starts to doubt the reality of this world-and even his own existence.