Shiraishi Tsubura just transferred to Ryuugabuchi Academy High and is trying to keep an extremely low profile. To live the normal high school life. But she's an amazingly talented baseball player who doesn't want anyone to know about it. Why is she trying to keep it a secret?

10 years ago, a mushroom-shaped alien spaceship landed on Earth, but the media began to lose interest in it as time went on and nothing exciting happened. Now, a change is coming. Tetsu is a student at the nearby high school, where he is one of the members of a science club that is in danger of being abolished. The club president, who he likes, is an active girl named Aoi. When an alien creature appears at their school, she convinces the club to sneak in after hours to have a peek at it. After she has a particularly close encounter with the alien, she begins to suffer from fever, memory loss, and the growth of an alien tail. An infectious disease agency comes to take her into custody, and it looks like hers is not the only case.