Half a year ago, a giant spiderweb appeared across the sky. For a while, it got a lot of media attention. Eventually, when nothing seemed to be happening, people carried on with their normal lives, ignoring the spiderweb. Amedome Tsutsuji lives his daily life under the spiderweb. At school, people have nicknamed him "Ninja," since it's so easy not to notice he's there. Even automatic doors won't acknowledge his presence by opening for him. But he can see what others can't: aliens are coming down from the spiderweb, taking humans bodies as hosts, and eating people.
For that reason, he uses his ninja-like ability to carefully guard his crush, Mizuno, as she goes home from school. In other words, he stalks her, but with the best of intentions. He's determined to be there to protect her when the spider-aliens attack. To that end, he teams up with another, friendlier alien named Tsuda, who gives him a powerful weapon: a faucet. Will Tsutsuji be able to protect Mizuno from the parasitic spider-aliens with his trusty faucet?