This Boy Can Fight Aliens (2011)

All of a sudden, the world was invaded by an alien race. One day, a member of Temporary Alien Counter-Measure Headquarters, Arikawa, finds a high school boy, Kakashi, who fell senseless, and lost his memories. For some reason, Kakashi has got a power, that is effective against the aliens like nothing else. He is taken care of by optimistic Arikawa and his superior, high and mighty Shiro, and so their queer life together begins. Four months passed since then. Kakashi is still fighting the aliens for the sake of his parents and friends, who surely live somewhere. Between Arikawa's kindness and Shiro's strictness, this carrot-and-stick policy makes him perplexed, but eventually he gets used to it. However, when Kakashi loses the reason for fighting, the situation suddenly changes.