In secret, alien parasites drift downwards toward Earth. Their directive: to take control of a human body and thrive in secret. When a parasite attempts to take over Shinji, an ordinary high school student, he stops it in his arm to save his mind. With the strange power of amorphous muscle, the curious parasite strikes an uneasy truce with Shinji: it will keep him alive and strong so that it may continue living, and will help protect him from the other parasites that might not take kindly to Shinji's mind still actively working. Can Shinji gain the courage to face the parasites and protect humanity? And would it even make a difference if he did?