The Kagemori family has secretly protected its neighbor, the Konnyaku family, for 400 years. Mamoru has been the protector of the daughter, Yūna Konnyaku, since they were in kindergarten. When Yūna is in trouble, Mamoru quickly puts on his ninja suit and transforms into a competent ninja, able to protect her from harm. Unfortunately, this poses quite a challenge as Yūna, being both clumsy and absent-minded, often stumbles into situations where Mamoru must once again come to her rescue.