Shinobu is a ninja apprentice trying to pass a ninja exam. Kaede is just a normal schoolgirl studying for a school exam. Their paths cross when Shinobu tries to sneak into Kaede’s room and steal her panties as part of the exam assigned to her by the lecherous yellow ball thing, Onsokumaru. Shinobu is a terrible ninja and Kaede can see her trying to steal and stops her. Shinobu starts to cry about her failed life and Kaede decides to let Shinobu take one pair back and a friendship is forged.
Descriptions taken from AniDB.net