Kagemori Mamoru is a dowdy boy whose hair is disheveled and wearing thick glasses. But actually he is the son of a ninja family. They have protected their neighbor, Konnyaku family, secretly for 400 years. Mamori has also protected the daughter, Konnyaku Yuna, since they were in the kindergarten. When Yuna is in trouble, Mamoru puts on ninja suit quickly, and he turns into a competent ninja to help her.