From DrMaster:
Yuji Midorikawa is your typical high school student whose has a secret identity: He is "Green" in the high school battalion unit, Gakusei 5 (G5 for short). G5 is the special unit trained to fight and protect Earth against the invasion of the dreaded Galactic force "Gurdark" and its sexy queen Mayura. But Green has a problem. He really can't fight, and always ends up hiding behind his other team mates. What ensues is a witty and wild ride as our "Imperfect Hero" struggles to maintain his reputation as a "guardian of earth" while keeping up his grade point average in school!